CA2099385C - Algaas native oxide - Google Patents

Abstract

A method of forming a native oxide from an aluminum-bearing Group 111-V
semiconductor material is provided. The method entails exposing the aluminium-bearing Group III-V semiconductor material to a water-containing environment and a temperature of at least about 375 °C to convert at least a portion of said aluminum-bearing material to a native oxide character-ized in that the thickness of said native oxide is substantially the same as or less than the thickness of that portion of said alumi-num-bearing Group III-V semiconductor material thus converted. The native oxide thus formed has particular utility in electrical and optoelectrical devices, such as lasers.

Description

WO 92/12536 PCT/LrS91/04512 _i-~.l.c~aAs Native Oxide This invention was made, in part, with Government support under contract DAAL 03 89-K-0008 awarded by the United States Army and Grants NSF ECD 89-43166 and NSF DMR
89-20538 awarded by the National Science Foundation. The Government has certain rights in the invention. This appli-cation is a continuation-in-part of U.S. patent application Serial No. 636,313 filed December 31, 1990.
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a method of form-ing a high quality, stable and compact :native oxide layer from an aluminum-bearing Group III-V semiconductor material.
T~lore specifically, the present invention forms the native oxide layer by a method involving wet thermal oxidation.
Importantly, the thickness of the native oxide layer produced by the method is substantially the same as or less than the thickness of the aluminum-bearing Group III-V material layer that converts to the oxide. Further, the present invention forms the native oxide under conditions that discourage the formation of various other oxygen-rich compounds, such as aluminum oxide hydrates and aluminum suboxides, the presence ~f which compounds cause an expansion oi: the resultant native oxide layer thickness and are generally deleterious to the electrical and physical properties of the semiconductors.
The present invention is also directed to devices utilizing the native oxide'layer thus grown, including elec-trical and optoelectrical devices such as transistors, ca-pacitors, waveguides and, more especial7.y, lasers.

WO 92/ 12536 '' - PCT/ L.TS91 /04512 ~~~~,~~ J
Finally, the present invention relates to the mash-ing and passivation of semiconductors utilizing the native oxide that forms from the practice of the present invention.

2. Description of the Prior Art An important trend in semiconductor technology is the use of Group III-V materials for the fabrication of semi-conductor devices. While the utilization of silicon (Si) is still prevalent in this area, Group III-V compounds --such as GaAs-- have been the subject of much research due to the significant advantages these compounds offer. For example, Group III-V compounds generally exhibit larger band gaps, larger electron mobilities and have the ability to produce light, which properties result in unique electrical and opti-cal characteristics.
Notwithstanding these qualities, Group III-V semi-conductor technology has failed to develop at the rate and to the level of silicon-based technology. The primary causative factor to this end has been the inability to produce, on the Group III-V semiconductor, an oxide layer of desired thick-ness that exhibits the necessary surface state and electrical properties required for practical application. In this re-gard, the oxide must be able to fulfill, without the disrup-tion and strain caused by over-expansion of the oxide thick-ness, a variety of functions in a practical and consistent manner. Examples of these functions include: serving as a mask during device fabrication, providing surface passiva-tion, isolating one device from another (dielectric isola-tion, as opposed to junction isolation), acting as a compon-ent in the anatomy of various device structures and providing electrical isolation of multilevel metallization systems.
Accordingly, the presence of a high-quality, stable oxide layer having adequate physical properties and proper thick-ness is essential to the successful development of Group III-V semiconductor technology.
Silicon-based materials, unlike Group III-V semi-conductors, readily form a high quality oxide (Si02) by such methods as reacting the silicon crystal with water vapor, .
e.g., in the form of steam. Indeed, the very existence of silicon-based integrated circuit technology is largely due and owing to this ability of silicon to form a high quality silicon oxide. Moreover, this oxide is a native (or natural) oxide, as opposed to a deposited oxide layer. Native oxides are more desirable than deposited oxides in that they are monolithic with the crystal and thus avoid potential mis-matching of dielectric characteristics and problems asso-ciated with oxide-substrate interface bonding, such as lift-ing and cracking. Further, deposition processes are on the whole more complicated and costly than are methods of growing a native oxide thus making the latter more attractive for commercial use.
Attempts at producing a ,qualit-y native o::id~ layer on Group III-V semiconductors by adapting methods that have been successful for silicon have had disappointing results.
These results are usually ascribed to the fact that the be-havior of Group III-V materials depends, in large part, on the behavior of the individual Group I:II-V constituents, which behavior, under given circumstances, may not be compat-ible with the desired end result. For example, thermal oxi-dation techniques, which are regarded to be among the sim-plest of the techniques and which have had tremendous success for silicon, have not worked well for Group III-V materials such as GaAs. This is because gallium (Ga) and arsenic (As) have different oxidation rates, and because the AsZ03 and 4 As20~ that are produced in the normal course of events, are ~~~9~~~ _.
WO 92/12536 PCT/US9l/04512 v~iatile: once formed, they tend to boil off the substrate rather than stabilize on it as part of an oxide layer.
Thus other approaches, which for the most part occur at low temperatures, e.g., room temperature, to avoid the formation of volatile components, to produce a native oxide layer directly from a Group III-V semiconductor surface have evolved. These techniques include the use of ozone, simultaneous OZ and electron beam exposure, photo-excitation of electron-hole pairs (in GaAs), use of more reactive oxi-dizers (such as N?O), photochemical excitation of the gas-phase molecular species, addition of water to the 02, excita-tion of 02 with a hot filament or a Tesla discharge, plasma excitation of the 02 a:.d exposure to a high kinetic beam of atomic oxygen. The drawback of these techniques, aside from their overall complexity, which makes them unrealistic for large scale utility, is that although they can increase the rate of formation of the first few monolayers of oxide they are (with the possible exception of plasma oxidation and exposure to a high kinetic beam of atomic oxygen) generally ineffective for rapidly growing layers having a thicknesj ir.
the range of hundreds to thousands of angstroms, A (10,000 A
- 1 micron, urn). Moreover, these oxidation reactions are often incomplete, the Ga and As not being in their highest formal oxidation state. The resulting oxide is thus usually deficient in Ga or As, which deficiencies have adverse ef-fects on oxide quality.
Particular examples of these methods include: U.S.
Patent No. 3,859,178 wherein an oxide is grown on the surface of a GaAs layer by submersing the GaAs layer into an anodiza-tion bath of.concentrated hydrogen peroxide (H202) having a pH of less than 6.

W092/12536 ~5 . PCT/US91/04512 'J.S. Patent No. 4;374,867 describes a method of growing an oxide layer on InGaAs by using a growth chamber that has been evacuated and in which an oxygen plasma has been established. Water vapor is introduced into the chamber to facilitate the growth process.
U.S. Patent No. 3;890,169 relates a method of form-ing an oxide on GaAs in an electrolytic fashion using H202 as an electrolyte. The oxide thus formed is rendered more sta-ble and more impervious to impurities and dopants normally employed in diffusion processes by being dried in oxygen at 250°C for 2 hours followed by annealing at 600°C for 30 min-utes.
U.S. Patent No. 3,914,465 describes a double oxida-tion technique whereby a native oxide is grown on GaAs by immersion in an aqueous H202 solution with a pH of 1.5-3.5, followed by a second oxidation in aqueous H2o2 at a pH of 6-8.
H. Barbe, et al. in Semiconductor Science and Tech-nol.ocrv, 3, pp. 853-858 (1988) describe the growth of a thin oxide layer on GaAs in methancl having a varying wate,_- con_ tent, without the application of external voltage. J. P.
Contour, et al. in the Japanese Journal of Applied Physics, Vol. 27, No. 2, pp. L167-L169 (Feb: 1988) report on the prep-aration of a surface oxide on a GaAs substrate by heating the substrate to 250° - 350°C in air. Similarly, in Applied P~sics Letters, Vol 26, No. 4, pp. 180-181 (Feb. 15, 1975), the growth of an oxide film on GaAs by thermal oxidation at 350°, 450° and 500°C is described. Applied Physics Letters, Vol. 29, No. 1, pp. 56-58 (July 1, 1976) reports on a one step dry process to form an oxide film on GaAs by plasma oxidation using an oxygen plasma.
Because of the complexity of these techniques and a the less-than-desirable results in terms of physicality and WO 92/12536 ~ ~'J ~ c~ 6 PCT/US91/04512 ch.ickness obtained, all of which can be related to the diffi-culties in worl~:ing with Ga and As, methods of oxide formation have been developed which involve overlaying or implanting on a Group III-V surface a material that can oxidize more read-ily. Aluminum (Al) and aluminum-bearing compounds are ex-amples of such materials. These particular materials are particularly adaptable in that aluminum is a Group III ele-ment and is known to oxidize more easily than the other ele-ments normally found in Group III-V semiconductors.
Examples of oxidation methods which exploit the presence of aluminum or aluminum-bearing compounds include U.S. Patent No. 4,144,634 which first deposits a thin layer of Al by, e.g., evaporation, over a GaAs substrate. The A1 overlay is then oxidized by plasma oxidation. Y. Gao, et al.
report in the Journal of Applied Physics, 87, (11), pp. 7148-7151 (June 1, 1990) a cryogenic technique whereby molecular oxygen is first overlaid on a GaAs surface; deposition of A1 follows. The A1 reacts to form an oxide layer until the oxygen is depleted.
C. W. Wilmsen, et al. in Thin Solid Fplms; ~1, gp.
93-98 (1978) report a method whereby a metal, such as Al, is implanted into a Group III-V substrate; oxidation then occurs by thermal or anodic means. M. Hirose, et al. relate in Physica Status Solidi, (a) 45, pp. P,175-K177 (1978) an oxi-dation process for GaAs in which oxygen gas, admitted close to the substrate surface, is reacted with A1 molecular beams to form A12o3. Finally, U.S. Patent Nos. 4,216,036 and 4,291,327, and European Patent Application 0 008 898 describe the fabrication of oxides by the thermal oxidation of an AlAs or AIGaAs layer which has been epitaxially grown on GaAs.
The oxidation occurs in a flowing gas mixture of 800 02 and 20o N2, and can occur in the presence of water vapor in order to permit the use of lower temperatures, e.g., 70°-130°C; the WO 92/12536 -~- PCT/US91/04512 ~~9~~~
oxides produced by this method ar~~, however, believed to be aluminum arsenic oxide and/or hydrated aluminum oxides.
These types of oxygen-rich 'aluminum compounds do not have the o requisite physical characteristics tlhat are necessary for semiconductor application; moreover, their presence in any modest amounts is deleterious to semiconductor structure. In addition to this, and integrally related to the presence of hydrator, is the expansion of thickness in the final oxide layer, which is consistently 80o thicker than the thickness of the original AlAs epilayer. In terms of real application and device construction, this magnitude of layer expansion is wholly impractical in that it distorts and strains the device architecture to unacceptable levels acrd puts inter-dependent dimensions and geometry out of kilter. These shortfalls are especially harmful when the semiconductor device is an opto-electrical device such as a laser, th.e optical output effici-ency and lifespan of which is highly dependent on proper crystal dimensioning and geometry as the various layers are developed over the course of device fabrication.
In brief , prior art i"et hods which rely on the pres-ence of materials such as aluminum, are either too complex f or large scale use or result in oxides that contain signifi-cant amounts of hydrates and/or have thicknesses which are over-expanded. The oxides produced by these methods also have less-than-desirable physical and electrical character-istics, in that they have poor electrical properties, e.g., significant leakage, and the overall quality of their physi-cal state is not good. As to the latt=er, oxides formed by these known methods exhibit non-uniformities in density and continuity, and also lack suitable stability, which results in lifting, cracking and out-diffusion; devices fabricated with oxides grown by these methods show a strong tendency to degrade in unacceptably short periods of time under normal conditions of use and atmospheric exposure. These undesir-able end results and deleterious effects thus preclude t:~e use.> of these methods in large scale practical application as required for commercial devices.
Thus the semiconductor art, although producing a variety of methods to form oxides on Group III-V semiconduc-tor materials, recognizes a continuing need for a method of growing an improved, high-quality native oxide on aluminum-bearing Group III-V semiconductor materials, particularly a native oxide whose thickness is substantially the same as or less than the thickness of the semiconductor material from which it forms. Moreover, it is desirable that the method be simple, cost effective and produce the native o::ide consis-tently in a controlled and repeatable manner.
SUMMARY OF THE INVENTION
A new method of growing a high-quality native oxide on an aluminum-bearing Group III-V semiconductor has now been developed. The native oxide thus grown exhi~its a proper range of conversion thickness and has superior physical and electrical characteristics as compared to oxides grown by methods known heretofore. Specifically, the native oxide layer grown by the method of the present invention has a thickness which is substantially the same as or less than the thickness of that portion of aluminum-bearing Group III-V
material from which it forms. The native oxide layer thus grown is denser and more stable than oxide layers formed from prior art methods, meaning, for example, that they do not degrade under conditions of normal use and atmospheric expo-sure. Further, the native oxide grown in accordance with the present invention manifests operating and performance char-acteristics that surpass those of any other currently used ~~r:ide film. For example, the native oxides formed from the present invention exhibit excellent metallizztion adherence and dielectric properties. The native oxides formed by the method of the invention are particularly useful in optoelec-trical devices, such as lasers, which can tolerate oxide a layer contraction but are acutely affected by over-expansion in oxide layer thickness. Lasers thus fabricated are capable of long-term, high power output before burn-out occurs.
In accordance with the present invention, a method of growing a native oxide on the surface of an aluminum-bearing Group III-V semiconductor material is provided. The method comprises exposing an aluminum-bearing Group III-V
semiconductor material to a water-containing environment and a temperature of at least about 375°C to convert at least a portion of the aluminum-bearing Group III-V semiconductor material to a native oxide. The native oxide is character-ized in that the thickness of said native oxide is substan-tially the same as or less than the thickness of that portion of said aluminum-bearing Group III-V :semiconductor material thus converted.
In further accordance with i:he subject invention semiconductor devices utilizing the native oxide thus grown are provided. Devices of particular applicability in this regard include electrical and optoelec:trical devices such as transistors, capacitors, waveguides and, more especially, lasers.
In still further accordance with the instant inven-tion the masking and passivation of se:miconductor5 utilizing the native oxide that forms from the present method is also described.

EFF:iRh DE~CRIF'TI023 OI' TF-;E DRAWINGS
Fig. l shows a thin platelet of disorder-defined red-gap AlAs-GaAs superlattice (SL1) discs surrounded by yellow-gap AlxGal-xAs (where x is about 0.8) after oxidation by the present invention at 400°C and 3 hours in are atmos-phere of nitrogen and water vapor. The top row of SL discs (representing a coarse-scale alloy) had e~:posed cleaved edges which were converted by the present invention to native oxide to a depth of 24 ~.un beyond the crystal edge (indicated by the small horizontal arrows). The oxide thickness of the 24~un region was substantially the same as the thickness of that portion of the original SL1 material that was converted. The oxide was transparent in appearance.
Fig. 2 shows an AlAs-GaAs superlattice (SL1) after oxidation by the present invention at 400°C and one hour in an atmosphere of nitrogen and water vapor. Oxide conversion into the edge region of the SL disc was 3 um (as indicated by small horizontal arrows). The oxide thickness of the Sum region was substantially the same as the thickness of that portion of the SL that was converted.
Fig. 3 shows an AlAs-GaAs superlattice (SL2) after oxidation by the present invention at 400°C and 4 hours in an atmosphere of nitrogen and water vapor. SL2 was a finer scale alloy than was SL1 and the oxide formation was 2-3 dun into the edge of the SL disc. The oxide thickness of the 2-3 Wn region was substantially the same as the thickness of that portion of SL2 that was converted. The slower conversion rate even at a longer time period relative to SL1 in Figs. 1 and 2 was due to the finer alloy scale of SL2.
Fig. 4 shows the photopumped room temperature (300°
f;elvin, K) laser operation of the red-gap SL1 discs of Fig. 2 which were oxidized by the present invention. The sample was ,~, compressed in an annealed copper heat sin) under a diamond window.
Fig. 5(a) is a scanning e:Lectron microscope photo-mic:rograph showing quantum well heterostructu.re (QWH); the lef t side of Fig . 5 ( a ) shows the QWF~ with an Si02 mash: ; the right shows the QWH with the GaAs cap removed. The exposed crystal where the GaAs cap was remo~~ed was oxidized according to the present invention at 400°C for 3 hours in an atmos-phere of nitrogen and water vapor. Fig. 5(b) shows the QWH
after the oxide on the right side wa.s selectively removed.
The slanted arrow in rig. 5(b) shows the crystallographic facet defined by the natural oxide on the AlvGal-BAs (x or abo'st 0 ~ 8 ) conf fining layer .
Fig. 6(a) shows the current versus voltage (I-V) characteristics for the contact on the GaAs cap layer of the left-side masked region (Si02 removed) of the QWH of Fig. 5;
Fig. 6(b) shows the I-V characteristic for the contact of the right-side, region having the native oxide as formed accord-ing to the present invention. Fig. ~(a) exhibits p-n conduc-tion and Fig. 6(b) an open circuit (I ~ Ol.
Fig. 7 shows the spectral behavior and the power versus current (L-I) characteristics of the QWH laser of Fig.
having the native oxide as grown according to the present invention at 20 milliamps, mA, 30 mA and 40 mA.
Fig. 8 shows the high power laser operation of the QWH laser of Fig. 5 which incorporates the native oxide as formed according to the present invention. Burn-out did not occur until over 100 milliwatts, mW/facet.
Fig. 9 is a photomicrograph showing the surface of a multiple-stripe contact region, as prepared using a native oxide that was f or;ned in accordance with the present inven-tion, on a AlxGa1-xAs-GaAs (x of about 0.8) QWH crystal.
Fig. 9(a) shows the native oxide as formed at 400°C for 3 WO 92/12536 -1 ~' PCT/US91/0451Z
h~~urs i_n an atmo.spheze'ol'nitrogen and. water vapor, on the upper AlYGa~ -3,As ( x, of about () . 8 ) conf fining layer ~,a;~ez a the QWFI was not: ma~l:ed by a GaAs contac t layer . Fi.g. 9 ( b ) shows the entire surface following m~tallization 4:ith titanium-plati.num-gold (Ti-Ft-Au).
Fig. 10(a) shows the neap:-ffield (tdF), and Fig.
7.0(b) thc~ far-fie7_d (F'F) emission patterns of the ten element Jrtl11t1p1E'-stripe ~WH laser array ShU47n 1:1 Fig. 9 which had 5 micron (um) wide emitters on 7 llm center-to-center spacings.
The narrow pea): with full angle at half power at 100 mA of 0.6° (Fig. 10(b)) indicated that the strips were coupled.
Fig. 11 shows the continuous-wave (cw) room-temper-ature (3U0° K) laser operation of the ten emitter QWH coupled array ~f Figs. 9 and J..O which had 5 um wide stripes on 7 um centers. The output power per facet approached 300 mW. In the inset, the spectral behavior tat 8457 ~ and 1.466 eV) of the diode is shown at an output power. of lO mW (115 mA).
Fig. 12 shows the high power operation of a ten emitter native-oxide coupled-stripe Al.l,Ga1-kGaAs QWH laser array. The stripe width was the sa:~e as t hat of t~iie array of Fig. 11 ( 5 dun) , but the stripes were located on 10 j.un cen-ters, as shown in the inset. Output powers exceeding 400 mW
per facet were obtained.
Fig. 13 shows a shallow-angle beveled cross sec-tion, after zinc (Zn) diffusion, of a 1.05 wn AlxGal-xAs-GaAs superlattice with 20 um masking stripes, (top) on the crystal surface. The masking stripes were comprised of a native ox-ide as formed in accordance with the present invention. The lower part of the slant cross section shows regions, not masked by the oxide, where the superlattice was disordered;
the disordered regions are shown as alternating with regions that were masked by the native oxide and where the super-lattice was intact.

F'i g . 1 ~~ shows tl~e cleaved section of a ( i00 ) AlxGa1-hAs-F.lyGal-yAs-AlZGa1-BAs QWH (x of a3~out O.F, y o about 0 . ?.5, z of about 0 . 06 ) ~>latelet sample. Native o::ide formed according to the process of the present invention, was revealed by removing the substrate and etching a tapered hole through all the layers (stopping at the oxide). The native ~t:.ide layer, indicated as Region A, transmitted light an~? was clear enough to show spocks of dirt 'that were on it. The upper confining layer is indicated as Region B; the QWH wave-guide and upper and lower confining :layers are indicated as Region C. The,entire QWH is indicated as Region D.
Fig. 15 shows the photopumped continuous wave (cw) room-temperature (300~ K) laser operation of the annealed QWH
of Fig. 14 which incorporated a native oxide as formed by the method of the present invention: Fig. 15(b) shows, in com-parison, the pulsed-excited laser operation of a non-masked bare sample as modified by impurity-induced layer disordering (IILD). Both samples had been simultaneously annealed at 575°C for 1 hour in a Zn diffusion ampoule.
Fig. 16 shows a scanning electron microscop' (;g~.~,) Image (using a stain) of a buried-heterostructure (BH) AlyC,a~-yAs-GaAs QWH laser of er Si di:~fusion at 850°C for o.5 hours and impurity-induced layer disordering on the left and right sides (indicated by the letter "n"). Oxidation accord-incT to the present invention, at 400°C~ and 3 hours in an atmosphere of nitrogen and water vapor, of the top confining layer was then performed. The Si diff:usion undercut the edge of the GaAs cap, which resulted in a contact region of about . 5 um and an active region of about 7 ~m ( f or a 6 lun masking stripe). The formation of a native oxide by the method of the invention was at. the surface of the exposed high-gap Al~_Gal-xAs confining layer, and extended completely to the w 14 - pCT/US91 /04512 edge of the Gams cap ( as indicated by the two unmar)~ed down-ward arrows).
F'icr. 17 shows the continuous wave (cwl room-temner-ature, (30f~° K) output (single facet) power versus current (L-I) curve and spectra for a:~ IILD QW~i laser diode, having a native oxide layer as formed by the method of the present invention. '.Che laser diode had a 3 ~m-wide active region (as compared to the 7 um wide active region of the laser of Fi.g.
16). The laser threshold (250 um long diode) was 5 mA, with single mode behavior well developed at 7 mA (~;avelength of about 8198 A). Spectral narrowing and "ringing" began at about 2 mA and caused the fuzzy appearance at the top ef curve (a) of the inset (3 mA).
Fig. 18 shows the near field (NF) and far-field (FF) emission patterns of a 3-arm-wide active region IILD QWH
laser, that was delineated by native oxides as formed by the present invention, under continuous wave (cw) excitation of 12 mA. The near-field (tZF) pattern indicated as (a), had a full width at half maximum power of about 3.4 ~.~.m. The far fif~ld ( FF ) pattern, i.,~ii~3ted as (b) , hau a iuii angle at half power of 20.9°, and was diffraction limited.
F.ig. 19 shows a Nomarslsi image photograph taken after 100 days of an AlAs-GaAs heterostructure which had undergone oxidation at atmospheric conditions, Fig. 19(a), and which had a native oxide layer as formed by the present invention, Fig. 19(b). The atmospherically oxidized Sample (a) shows the characteristic roughening of atmospheric hydro-lysis, while Sample: (b) oxidized by the method of the inven-tion was covered with a smooth "blue" oxide and was unaf-fected by the aging process.
Fig. 20(a) is a scanning electron microscope (SEM) image (unstained cross section) of Sample (a) of Fig. 19 W0 92/12536 ~ i S'~ PCT/US91/04512 ,a° ~~~~i~~~
att~:t being cleaved and aged ('for,it)U days). Fig. 2U(b) is a SEM image of Sample (b) of. Fig. 19 after being cleaved and aged (for 100 days}. Sample (a) had been chemically attacked tc~ a depth of 1 u.m ( indicated by vertical arrows } and was striated in appearance. In contrast:, Sample (b) remained smooth under the native o~.ide layer which was less than 0.1 urn thick. This thickness was less than the thickness of that f>ortion of heterostructure which had. converted to the oxide.
Fig. 21 shows secondary ion mass spectrometer (SIMS) profiles after Sample (a) and (b) of Fig. 19 were aged for 80 days. In accord with the SEM images of Fig. 20, a Ga depletion approximately 1 ~ deep in Sample (a) was not evi-dent in Sample (b). Also in accord 'with Fig. 20, Fig. 21 shows that chemical attack was about 1 um deep for Sample (a}; no chemical attack at this depth was evidenced in Sample (b).
DETAILED DESCRIPTION OF THE INVENTION
The present i n«entl0n pr~~,~.d~g a mCth Od of forming a high-quality native oxide from a Group III-V semiconductor material where the thickness of the native oxide i.s substan-tially the same as or less than the thickness of that portion of said Group III-V semiconductor material which is converted to the native oxide. The native oxide formed by the present invention is especially utile in the fabrication of electri-cal and optoelectrical active devices, including capacitors, transistors, waveguides and lasers, such as stripe-guided lasers, surface emitters and lasers whose active regions, as normally defined by their quantum well structures, are slightly mismatched in order to lengthen the wavelength of the energy emitted. An example of su~~h a device is one hav-WO 92/12536 1 s PCT/US91/04512 lng a f lrst quantum wc_ll 'i c>rmcd of , a . g. , InGaAs inside of a second quantum well formed of, e.g., GaAs. The native oxide formed by the method of the present invention can also be used to define various geometries and patterns on the sur-Faces of Group III-V semiconductor materials in order to create any number of different configurations and topologies.
The method of the present invention finds particular utility in forming a native oxide from an aluminum-bearing Group III-V semiconductor material.
Although the scope of the present invention is independent of any theory explaining its superior results, it is theorized that the present invention forms the native o:,ide in a manner that discourages the formation of debilitating amounts of hydrated and/or oxygen-rich aluminum compounds that are believed primarily responsible for the increase in thickness of native oxide layers grown in accordance with wet thermal oxidation techniques known heretofore, relative to the thickness of that portion of aluminum-bearing material so converted. In another aspect, it is believed that the present inventio_n_ forms the native vxiue izi a manner that favors the formation of sufficient amounts of anhydrous forms of aluminum oxide and/or aluminum oxide hydroxides (referred to herein as dehydrated aluminum compounds) such that the thickness of the native oxide layer thus formed is substantially the same as or less than the original thickness of that portion of the aluminum-bearing Group III-V material converted to the native oxide.
As to the aforementioned oxygen-rich aluminum compounds, these include, e.g., compounds having the formula A10, A120 and A12o2. These compounds, which are deleterious t.o semiconductor performance and stability, are referred to herein as aluminum suboxides.

WO 92/12536 ~ I ~ - PCT/US91 /04512 h~' ~f~?T-~'ment.~or~~d hvdrat:.ed compounds that-. arc r>el.ieved to form in undesirable amounts when employing wet t~»rmal o::idation methods known heretofore, and are accordingl~~ believed to contribute to the poor quality and increased thickness of native oxides thus formed, include aluminum hydroxides and aluminum oxide hydrates as hereinbelow defined.
As t0 alumiIlum hydroxides, the most well-defined crystalline forms include the three trihydroxides having the general formula A1(OH)3, which are conventionally denominated as gibbsite (also known as hydragillite in European literature), bayerite and norstranditn. The deleterious effects of these aluminum hydroxides relative to semiconductor application are believed related ~to the triply hydroxylated status of the aluminum.
As to the aluminum oxide hydrates, these are formed from the intermediate or transitional forms of aluminum oxide; A1203. These intermediate forms, individually unsuited for practical semiconductor purposes, are generally i.den rifled as : '~ -A1_ p ~y _Al n ~ T ~ ~~ , ~-A i2'v3 , k-A12o3 j , ,.
and L,-A120.~. These intermediate species of aluminum oxide normally exist between the compositional range of true anhydrous aluminum oxide and the hydroxide forms of aluminum.
Accordingly, some of these intermediate species can form hydrates of the formula A1203. nH20 (O<n<0.6). It is the hydrates which form from these intermediate aluminum oxides that are referred to herein as aluminum oxide hydrates. It is further believed that the greater the degree of hydration, e~g., trihydrate versus monohydrate, the greater the degree of. expansion in native oxide layer thickness.
One technique of determining the extent of hydration in an oxide layer is by meas~r,ring the index of refraction (denoted as "n"), which those of skill in the art tail? appreciate as c:orrelatab~.e to dielectric constant. As a rule, the larger the index of refraction, the greater the dogree of hydration of the oxide layer and the more unsuitable that oxide is f.or practical semiconductor application. Thus the index of refraction for hydrated aluminum compounds such as, e.g., aluminum o3:ide hydrates, is generally in the range of about 2.0 to about 11Ø In comparison, the index ~f refraction for anhydrous oxides is generally in the range of less than about 2.U. For example, a dehydrated film of GaAs-oxide formed by gas plasma c~xid.atioc~ has m index of refraction, as measured by conventional ellipsometer techniques, of about 1.78 to about 1.87; dehydrated arsenic oxide (AsG03) has an index of refraction of_ about 1.93. Generally, anhydrous aluminum oxides and aluminum oxide hydroxides have an index of refraction of less than about 2Ø
In addition to forming the native oxide in a manner that discourages the formation of debilitating amounts of hydrated ~~nd/or oxygen-rich aluminum compounds as hPreinabeve described, it is beiiPVed teat the ~r~ser,t invention forms the native oxide in a manner that favors the formation of sufficient amounts of anhydrous forms of aluminum oxide and/or aluminum oxide hydroxides to thus obtain a native oxide having the requisite physical and electrical properties required for practical semiconductor application, as well as a thickness that is substantially the same as or less than the thickness of the aluminum-bearing material that is converted to native oxide by the practice of the present invention.
In this regard, a native oxide thickness that is substantially the same as or less than the thickness of the aluminum-bearing material that is converted can be measured, for purposes of the present invention, by the ratio of native WO 92/ 12536 ' 1. 9 - PCT/US91 /04512 u~:ide tti.ic~:ness to the thic~:ness of t:he aluminum-bearing material thus converted. As contemp3.ated by the present invention, this ratio is within the range of between about 0.G to about 1.1 (representing a shrinkage of the native oxide layer compared to the portion of aluminum-bearing material so converted of about 400, t;o an expansion of the seine of about 10 ~) without adversely affecting the physics of the native oxide formed:
As to the anhydrous forms of aluminum oxide, these . include a,-A1z03 and ~ -A1203. It is important to the appreciation of the present invention, to understand that stoichiometrically there is only one oxide of aluminum --namely, A12O3-- and that this oxide is polymorphic: it eyists in a variety of crystalline forms which have different structures, most of which, such as e.g., the intermediate aluminum oxides identified hereinabove, are substandard insofar as useful semiconductor-related electrical and physical properties are concerned. Generally, the forms of aluminum oxide that manifest the highest degree of parameters iWCcssary fvr practical sen~icvnC3iit:tor applicati~il ale ti'1~
anhydrous forms, including a-A1203 and. ~-A1203.
For- example, a-A1203 .has a well-defined, close packed lattice arrangement, and exhibits extreme hardness, stability, resistance to wear and abrasion, chemical inertness (including insolubility in, and unreactivity toward, water), outstanding electrical properties (such as dielectric character), good thermal shock resistance, dimensional stability and high mechanical strength.
As to aluminum oxide hydroxides, these include the two well-defined crystalline phases having the general formula A10(OH) which phases are convE:ntionally denoted as diaspore and boehmite.

WO 92/ 12536 ~ ~ 2 ~ PCT/US91 /04512 I ~. i s t~el i eveci tluat the native oxide formed in the gracticc: of the prosent, ~invc:ntion is formed in a manner such t3~at suffic:LCnt amounts of the anhydrous forms of aluminurc~ oxide and,~or aluminum oxide hydroxides result, rather than debilitating amounts of the hydrated and/or oxygen-rich aluminum compounds, and further believed that this circumstance is manifested in the fact that the thickness of the native o:,i.de formed in the practice of the ~~rosent invention ~.s substantially the same as or less than tlne thickness of the aluminum-bearing material that is so converted.
Molar volume serve~~ ;:. an indicator in this regard.
That is, the fact that the thickness of the native axide of the present invention is substantially the same as or less than the thickness of that portion of the aluminum-bearing mater:i.al treat converts to the native oxide is believed to indicate that the present invention farms a native oxide of compounds that have a molar volume substantially the same as ur less than that of the almnimun-bearing Group III-V
SCmICOnduCtOr materi 31 from lr7h.l.Ci: t he iiati'vC 'vYide forms.
Molar volume can be established from the following formula:
Molar Volume = Molecular Weight - Density The molar volumes for AlAs (an aluminum-bearing Graup III-V material contemplated by the instant invention), a-A1203 and ~-A1203 (anhydrous forms of aluminum oxide, as defined by the present invention), diaspore (an aluminum oxide hyd.ro::ide, as defined by the present invention) and gi.bbsite (an aluminum hydroxide, as defined by the present invention) and aluminum mono- and tri-hydrate (aluminum oxide hydrates, as defined by the present invention) are listed in Table 1; below:

WO 92/12536 21 - PCT/US911045t2 ~~~ ~ig~

Ti:t3LE J:

Molar thvlecular Substance Weiaht, a Density, yolume, alca c/mol c n-A1203 101.96 3.5 - 3.9 29.1 - 26.1 ~j-A1203 101.96 3.97 25.7 gibbsite, A1(OH) 78 2 _ . 32.2 diaspore, A10(OH) 60 :l 3 - 3' . 18.2 - 17.1 .

aluminum trihydrate, 156 2 . 6s.5 aluminum monohydrate, 199.98 3 ' 014 g . 3 A1203. F120 ,8 AlAs 101.90 3.73 27.3 GaAs 144.64 5:316 27,2 As seen by reference to Tab_Le 1, the molar volumes of the anhydrous forms of aluminum ox»de, a- and ~ -A1203, and the aluminum oxide hydroxide, diaspore, are substantially the same as or lE:SS than that shown for AlAs, thus indicating that an oxide formed from AlAs in practicing the present invention, wherein the native oxide ha.s a thickness substantially the same as or less than that portion of AlAs form which it forms, may be comprised primarily of dehydrated aluminum compounds, i.e., the anhydrous forms of aluminum oxide and/or aluminum oxide hydroxide. In contrast, when the thickness of the native oxide formed from AlAs is greater than that portion of AlAs thus oxidized --as in the case in earlier attempts at producing a native oxide, such as by methods embodied in U.S. Patent Nos. 4,,216,036 and 4,?_91,327-- this is believed to indicate that the native ~xi~e thereof is comprised primarily of compounds whose molar volt.une i.s greater than AlAs , such as , a . g . , aluminum monohydrate, aluminum trihydrate, and gibbsite --an aluminum hydroxide.
irr~ilar to aluminum, gallium also forms a.n oxide, Ga20.~, that has a variety of crystalline forms; these cry-stalline modifications are denoted a-Ga?,03, 8-Ga20.~, -Ga2U3, d -Ga203, e-Ga203. Of these, B-Ga203 is the most stable and best suited for semiconductor use. Further, under proper circumstances, aluminum oxides, such as a-A120.~, and gallium oxides, such as B-Ga?03, can form a solid solution and can form compounds of the formula GaAlO.~.
In the practice of the present invention, a native oxide is formed from a Group III-V semiconductor material;
preferably an aluminum-bearing Group III-V semiconductor material such as, e.g., AlGaAs, AlInP, AlGaP, AlGaAsP, AlGaAsSb, InAIGaP or InAlGaAs.
In a practical embodiment of the present invention, the alumini:m-bearing Group III-V semiconductor material is overlaid on the surface of an al~~min~,:,~"-free Group III-V semi-conductor material such as, e.g., GaAs, GaP, GaAsSb, InGaP or InGaAs. When the thicl>ness of the aluminum-bearing overlayer iS IlOt :;o great so as to impede the diffusion of the neces-s~~?-y oxidation reactants down through the entire aluminum-bearing layer, the conversion of the aluminum-bearing layer t_o the native oxide layer will essentially terminate at the aluminum-free Group III-v interface, or when the aluminum content of a given layer or interface 1_ayer is about 300 or less, e.g., x is about 0.3 in material such as AlxGal-xAs.
Diffusion effects, which can eventually terminate the oxidation reaction, normally become a factor when the aluminum-bearing material has a thickness of about 10,000 or more.

WO 92/12536 ?' PCT/US91/04512 Tt~c method ~f the present invention entails expos-:incr the aluminum-bearing Group ILI-V' semiconductor material to an environment. that contains water, preferably in the form of water vapor. In the preferred practice of this embodiment of the invention, the water vapor is present with one or more inert gases, such as nitrogen: The water vapor is also pre-ferably present in an amount wherein the nitrogen or other inert gas or gases is substantially saturated with water.
The water-containing inert gas environment is preferably, but need not be, under a condition of flow. When under flow, the rate should be at least about 0.5 standard cubic feet per hour (scfh), preferably about l.0 - :3.0 scfh; most preferably about 1.5 scfh.
In practicing the present :Lnvention, ~a temperature of at least 375°C is employed. Although no specific time period need elapse in order for the native oxide to form in the first instance, certain practices in this regard are preferred, especially in applications involving the more typical aluminum-bearing Group III-V semiconductor materials, such as A1~Gal-XAs where x is about i~.7 o_r greater-Thus in a first embodiment of the present inven-tion, wherein the temperature employed is in the range of from about 375°C to about 600°C, preferably in the range of about 390° C to about 500°C, more preferably in the range of about 400°C to ai~out 450°C, it is preferred if the exposure to the water-containing environment is for a time period of about 0.1 hour to about 6.O hours. A more preferred time period far this first embodiment is about 1.0 hour to about 5.0 hours; even more preferred is a time period of about 2.0 hours to about 4.0 hours. Most preferred for this first embodiment is a time period of about :3.0 hours.
In a second embodiment of the present invention, referred to herein as rapid thermal processing, a temperature WO 92/12536 ~ z 4 ~ PCC/US91/04512 ,~z .i.n ~..lm 1 mr~c~c~ c~f ov:~r abc~m GOU°C t~~ about 22UU°C. is emplolTed.
I n a yre,i_-err ed aspect of tlni.s second embodiment, the tomnerature employed is in t.hc range of about 650°C to about 1000°C; more: preferably about 700°C to 900°C and most preferably about X00°C.
In the practice of this second embodiment of the ~.>resent invention the exposure to the water-containing environment will depend upon whether the material is self-capping under the conditions employed. If not, exposure is preferably for a time period of up to about 120 seconds.
A more preferred time period for this second embodiment is about 5 seconds t.o about 90 seconds; even more preferred is a ti~«e period of about 10 seconds to about 50 seconds with the most preferred time period for this second embodiment being about 15 to about 30 seconds.
The time periods preferred in the practice of this second embodiment of the present invention are abbreviated to account for the fact that certain Group III-V materials, such as arsenic, have a tendency to evaporate at the higher tem-peratures employed therein. Thos the short exposure tim2S
fc>r these materials that are not self-capping are preferred in order to prevent or minimize any such losses.
In the practice of the present invention, particularly in the practice of the second embodiment described hereinabove, material to be oxidized in accordance therewith may be exposed to the aforedescribed temperatures in the first instance, or alternatively, may be heated to these temperatures from a lower temperature, e.g., room temperature (about 20° - 25°C) in heating apparatuses, such as conventional annealing furnaces or ovens, that are capable of reaching these temperature ranges in about 2 seconds or less, preferably in about 1 second or less.
In any event, in practicing the present invention the temperature need not be hci4 co:~stant. Thus for example, 2a~~a~~
WO 92/ 12536 ~ ' ' - PCT/US91 /04512 within the ranges elucidated above the temperature may be ramped up or down. These t.ernperatune ranges axe believed to discourage any appreciable formation of hydrated aluminum compounds and/or aluminum subo:sides iri quantities that would deleteriously affect the final oxide and its utility for semiconductor purposes. At the same time, these temperature ranges are believed to encourage the formation of the desirable anhydrous forms aluminum o:y:ide, such as a-A1?03 and/or aluminum oxide hydroxides, such as diaspore.
Other processing may occur subsequent to exposure of the aluminum-bearing Group III-V material to the water-containing environment without detrirnentally affecting the native oxide that has formed. Thus t=he native'oxide and the structure or article on which it has formed may be dried by removal from, or removal of , the water-containing environ-ment, with heating being continued at: the same or different temperatures than those used to form the oxide. Inert gas may also be passed over the native oxide-containing structure to facilitate drying. For example, in a flowing water vapor-nitrogen (or other inert gas) system at a temperature of, e.g., about 400° to 450°C, the flow of.water vapor into the system may be stopped after, e.g., 0.25 hour; the flow of nitrogen gas continuing however for a period of time there-after, e.g., 2 hours. The temperature of the flowing nitro-gen system may be the same temperature as used during oxide formation, or the temperature can be :ramped up or down, e.g., from 450° to 500°C.
Other processing that can occur subsequent to oxide formation and which has no ill-effect on the quality of the native oxide includes annealing. As conventionally preformed for_ Group ILI-V semiconductor materials, annealing takes place under "dry" conditions; that is in the absence of water. Dry conditions in this regard normally entail the use WO 92/12536 ~ ? '~ PCT/US91/04512 o.f an )s? ~~ar environment. ~~nnealing can also take place under an ovrr-~~re~ssure formed of materials having a tendency to vaporize at the thermal conditions employed to anneal.
Thus the native oxide-containing structure may be sealed in an ampoule having, optionally, an overpressure of arsenic or phosphorous; the former being normally used for arsenic-containing Group III-V semiconductor materials (such as AlGaAs) the latter for phosphorous-containing Group III-V
semiconductor materials (such as InGaP). Annealing is in either case generally performed at a temperature of about 600°C to about 850°C, preferably in the higher temperature ranges, e.g., 850°C, for a time of about 0.25 hour to about 4 hears, normally.
The .fol7.owing Examples are given to illustrate the scope of the present invention. Since the Examples are given for illustrative purposes only the invention should not be limited thereto.

2fl_9fl~8 WO 92/ 12536 2 ' - PCT/US91 /0451 Z
F~~AMPLF' 1.
OY>>IUA~~ION OF' A1',Ga As-AlAs-GaAs 1. - x 9UANTUM WELL ~IETEROSTRUCTURES ArdD SUPERLATTICES
AlAs-GaAs superlattices (S:Ls) were grown by metal--organic chemical vapor deposition techniques, as described by R. D. Dupuis, et al. in Proceedings c~f the International Symposium on GaAs and Related Corwounds, edited by C. M.
Wolfe, (Institute of Physics, London,, 1979), pp, l-9 and by I~1. ,7. Ludowise , J . Appl . Phys . , 58 ,W31 ( 1985 ) . Several SLs were employed, each about i micron (Lun) thick. Superlattices denoted as SL1 had AlAs barriers having an LB size of about 1 ~0 ~~, and Ga7ss wells of width LZ of about 45 A~. Superlat-tices denoted as SL2 had an LB(AIAs) of about 70 A and an Lz ( GaAs ) of about 30 ~,. Although sub>erlattices have a spe-cial character, i.e., sine quantization, they are also re-garded as being relatively "coarse", i.e., non-stochastic, AlyGal-xAs alloys. In this Examp)_e, SL1 was roughly two t vmes coar ser than SL2 . SL1 and cL~ ..,; ~-~. r , ", ~, "1~1. ~ l~u ~ surfaces, were rendered into random, or fine scale alloys, in a pat-terned form by impurity-induced layer disordering (IILD) by zinc (Zn) diffusion from ZnAs2 at 575°C for 0.5 hour as described by D. G. Deppe, et al. J. App).. Phys , _64, R93 11988) and W. D. Laidig, et al. Appl. phys. Lett., 38, 776 (1981).
The SLs were masked with Si02 discs having a dia-meter of about 37 dun. The discs were deposited by chemical vapor deposition and patterned (by standard photolithography) i.n a rectangular array on centers of about 76 Wn. After the Zn diffusion and the removal of the masking Si02, as well as the removal of the crystal substrates (by standard methods of WO 92/ 12536 ' '' PCT/US9t /045 t 2 mc.riuanical ldpping.and wet chemical etching), completely smooth, yellow gars Al~,Gal-',As platelets (having a thickness of about 1 'un) with red gap SL discs ( having diameters of about 37 um) distributed in a uniform array were obtained, as described by td. Holonyak, et al., Appl. Phys. Lett., _39, 102 (1981). The "fine" scale (yellow) and "coarse" scale (red) alloy, were now all in one sample, which sample was oxidized according to the method of the present invention: The sam-ples were heated in a furnace at 400°C for 3 hours in an H20 vapor atmosphere obtained by passing N2 carrier gas (with a flow rate of approximately 1.5 scfh) through an H.,O bubbler i-that was maintained at 95°C. The sample thus obtained by th:Ls method formed a native oxide having smooth, shiny sur-faces, which were much shinier than before oxidation. This surface characteristic was indicative of a dense, compact oxide that was substantially free of alumina oxide hydrates, and that a major component of the native oxide thus formed was likely an anhydrous aluminum oxide, such as a-A1?03.
A cleaved section of SL1, which was oxidized ac-tor ding to the invent i on is sho;.;.~. ; ~ ~; -- , '~,_ -~.. i .iy . t . lFle LOp edge o~
the 37 um diameter SL discs was cleaved and arranged so to expose the edge of the SL samples (the discs) to the oxida-tion process of the present invention. The bottom row of discs was uncleaved and hence was exposed to the oxidation process of the present invention only at the surface (front and back). As Fig. 1 shows, the conversion of the cleaved SL
discs to the native oxide was to a depth of about 24 um as measured from the edge of the SL (as indicated by the small horizontal arrows). This oxide thickness was substantially the same as the thickness of the cleaved, exposed SL that was converted. No expansion of thickness for the native oxide layer was seen. As to the bottom row of discs, only a slight WO 92/12536 ? ~ PCT/US91 /04512 delineation of oxidation was evident on the periphery; some surface oxide was also present. Thus after oxidation by the method of the present invention, the upper row of discs ap-peared solid and were nearly totally clear across each disc, while the surrounding IILD Al~Ga1-xA.s (where x is about 0.8) material remained yellow in appearance and the bottom row of discs (SL1 with oxide surface) remained red.
By reducing the time of the oxidation process from 3 hours to 1 hour (all other parameters were the same), the edge oxide conversion of an SL1 disc was to a depth of about 3 u.m as measured from the edge of the SL as shown in Fig. 2 (as indicated by the small horizonta:L arrows). This depth (or thickness) was substantially the same as the depth (or thickness) of that portion of the SL disc that~was converted to the oxide. No expansion or increase in the oxide thick-ness relative to the original SL thickness was seen. In Fig.
3, an SL2 (L~ + LZ being about 100 A) was oxidized for 4 hours, as opposed to the 3 hours in the case represented by Fig. l.. Edge oxidation of an SL2 di~~c, which is a finer-scale alloy than that represented by SL1, r~aS to ca dept h of ~-~ 4,U't1 as measured from the edge of the SL, even with the longer oxidation time. Nevertheless, the 2-3 llm oxide depth was substantially the same as the original SL thickness that was converted to oxide. No increase or expansion of oxide depth (thickness) was seen. The surrounding yellow gap AlxGal-xAs material (where x was about 0.7) IILD alloy oxidized also, but not nearly as extensively; oxidation here was hardly noticeable at all except for the shiny surface. Thus a dif-ference in the oxide conversion of (AlAs)x(GaAs)1-x alloy is seen when progressing from a coarser scale to a finer scale alloy, with random alloy and lower compositions converting much "slower". In all cases, however, the thickness of the WO 92/12536 ~.g .3~ PCT/US9t/045t2 ~5:ide formed by r-he n~ct2uod of the invention was substantially ty same as the thic~;ness of that por tion of the alloy tha t converts to the o~:ide .
F'.ic~s. 1~-3 also show that there is major anisotrop;l in h041 the o3:ide developed Un ( AlAs ) x ( GaAs ) 1-X SLs. O::i~da-tion normal to the layers was much "slower" than along the layers, and began to approach or become equal when the scale of the SL was finer. This is seen by comparing Fig. 3 (SL2 with LB + LZ approximately 100 A) with Fig. 1 (SL1 wit.u LF +
L approximately X00 rg.) .
z.
Thc~ high duality of the oxide produced by the met-hod of the present invention was demonstrated by way of a photopumped laser. F'ig. 4 shows the photopumped laser opera-tion of one of the inner (seal.ed edge) SL1 discs of Fig. 2;
the sample was heat sunk compressed in annealed copper under a diamond window by conventional methods. The laser opera-tion (at 300° k) of this SL sample was possible even with the loss, by oxidation, of some of the layers on both sides of the red gap SL disc, and even with some oxidation non-uniformity at the disc peripr~ery because of the crystal a::d doping difference (heavily p-type edge). It is believed that these results are attributable, at least in part, to the fact that the thickness of the native oxide produced was substan-tially the same as the thickness of that portion of_ the cry-stal that was converted to the oxide. That is, because the thickness of the native o~>ide thus formed was substantially the same as that portion of the SL layer that converted there was no appreciable distortion of the laser structure, meaning that high performance operation was possible.

WO 92/12536 " ~ n " PCT/LjS91 /04512 J'.;~:11t~9PT.F:. 2 NA'.L'IVE OXIDE-DEFINED SINGLE STRIPE GEOI'IETRY
tll .Ga. As-GaAs QUA2dTUIfi YELL HETEROSTRUCTURE LASERS
The use of native o ides f ormed in accordance with tree present invention in the fabrication of gain-guided oxide-stripe quantum well heterostructure (QWH) lasers was investigated. These devices, formed by simplified process-ing, were found to have outstanding performance character-istics which were directly attributable to the quality of the native oxide and the fact that the thickness of the oxide was substantially the saime as that portion of the cr~Tstal that was converted; thus the laser structure was not~distorted or strained as would happen if the oxides thic?mess expanded.
The epitaxial layers for these laser structures were grown on n-type (100) GaAs substrates by metalorganic chemical vapor deposition (MOCVD) as described in the Dupuis, et al. reference cited in Example 1. An AlO,RGa~,2As lower confining layer was grown of er a first GaAs buffer layer.
The active region of the gWH was grown next; the active re-gion consisted of symmetrical A10,25G~a0.~~As waveguide layers (ur~doped; thickness of these layers was approximately 1000 on either side of a Gags quantum well (QW) which had a thick-ness of about 400 A. Lastly, at the i~op of the QWH, a p-type A10.8Ga0.2As upper confining layer was grown to a thickness of about 9000 X~. The entire'QWH was then capped by a heavily doped p-type GaAs contact layer havincJ a thickness of about 800 A.
Diodes were constructed by first depositing, by chemical vapor deposition (CVD), about 1000 A of Si02 on the crystal. surf ace. Using standard photolithography and plasma WO 92/12536 ~ , -32- PCT/US91/04512 etching techniques, SiU s~.ripes, lU u.m wide, were defined on tlue wafer surface for purposes of masking. The crystal was then etched in Y..,SO~': HZU~ : Ii?O ( i : 8 : 8 J ) to mmove the GaAs G
contact layer in areas not protected by the Si0_, masking stripes. Except in the 10 um wide stripe regions, this ~:xposed the high composition Al Ga. As (x of approximately x 1-X
0~8) upper confining lay~:r. A native oxide was then formed in accord with the method of the present invention from this e::posed hig;~ aluminum-bearing composition of the upper confining layer. The QWH crystal was heated to about 400°C
for 3 hours in an H20 vapor atmosphere produced by passing an N~ carrier gas (at a rate of about 1.4 scfh) through an H.,O
bubbier maintained at about 95°C. About 1500 ~~ of the exposed AlxGa1-xAs (x of about 0.8) layer was converted to native oxide. The o?:ide thus produced by this method had a thickness of about 1000-1500 X~ which was substantially the same or less than the thickness of that portion of the exposed upper confining layer that was converted, and was clear and transparent and uniform blue in color (the blue boing caused by optical effects). Foiiowing oxidation, the Si02 masking layer was removed by conventional plasma etchina_ (CF4 and 4~ 02). The native oxide was unaffected by the plasma removal of the SiO~ layer.
Figure 5 shows a cross section of the crystal before removal of the Si02 masking layer. The vertical arrows in Fig. 5(a) indicate, as labeled, the thicknesses of the Si02 layer (left side) and of the native oxide layer (to the right). Fig. 5(b) shows a cross section in which the native oxide (right side) has been removed by etching in a KOH-Y,3Fe(CN)~ mixture. The pair of vertical arrows in Fig.
~(v) indicates the location of the oxide prior to removal.
Figure 5 illustrates that the oxidation method of the present WO 92/ 12536 - 3 3 - PC'T/US91 /04512 2~~~~~
.;.nveWicrti is somewhat sensitive to crystal orientation. For example, reference to Fig. 5 shows i;:hat where the oxide undercut the Si.02 masking stripe and the GaAs contact layer, a tendency existod to develop a crystallographic step on the AlyGal-xAs (where x was about 0.8) c:onfi.ning layer. This is shown by the small slanted arrow in Fig. 5(b). This sensitivity to crystal orientation :Lndicates that the native oxide integrally conforms to the underlying crystal structure which means that bonding problems at the interface would be minimized or eliminated:
After the Si02 masking stripes were removed, the crystal was sealed in an ampoule for. shallow Zn diffusion (ZnAs source, 540°C; 25 min) to increase the GaAs stripe contact doping. The crystal was them metallized with titanium-platinurn-gold. (Ti-Pt-Au) across the native oxide onto the exposed GaAs contact stripc-:. The metallization adhered onto the native oxide much better than on oxides or other dielectrics formed by prior art methods where the metallization frequently peels. After the p-type side ii~etaiiication, the crystal was thinned ( to 100 dun) from the substra;.e side and was metallized on the n-type side with germanium-gold-nickel-gold (Ge-Au-Ni.-Au). The wafer was then cleaved into Fabry-Perot bars, saw-cut stripe-contact sections were attached to copper heat sinks with indium (In) for continuous wave (cw) laser operation at room temperature, i.e., 300° K. Similar saw-cut sections with no contact stripes were prepared in order to investigate the blocking behavior of the o~:ide .
Figure 6ia) shows the current versus voltage (I-V) c~~aracteristic of a diode prepared on the QWH crystal in the GaAs contact stripe region; Fig. 6(b) shows (same scale) the open-circuit diode that resulted when no contact strips was WO 92/12536 ~ ' '1 PCT/US91/04512 present (i.t,., tle case of contact to a saw-cut section with only the native o::ide on the crystal).
The high duality of those laser diodes was demon-strated by their operating characteristics (continuous wave at 300° K). The diodes (having a cavity approximately 500 dun long) approached threshold, as shown in Fig. 7 by spectral curves labeled (a) 20 mA, (b) 30 mA, and (c) 40 mA. The cor-responding points on the power versus current (L-I) curve are shown in the inset of Fig. 7. The power versus current char-acteristics exhibited a rather sharp corner, reminiscent of a distributed feedback or cleaved-coupled cavity diode. This suggested that the oxide, unlike those formed by method of the prior art, perhaps because of. its sensitivity to crystal orientation, rippled or "milled" the crystal surface and prcwided some natural distributed feedback. As the diode approached threshold (Fig. 7) little tendency for multiple mode operation (spectral "ringing") was shown. Spectral curve (b) of Fig. 7 (30 mA) exhibited narrowing but no "ring-ing", and just above threshold a single mode was dominant as shown, in Fig. 7, at the higher current, (c) ~=0 mA.
Because of the quality of these recessed oxide single-stripe diodes and the excellent adherence of the met-allization on the natural oxide, they are easily attached with indium to a copper heat sink on the oxide side, thus providing very effective heat sinking in close proximity to the QWH active region. Figure 8 shows the high power contin-uous wave laser operation that was possible. The power out-put per facet exceeded 100 mW before burn-out occurred.
Besides the high performance capability demon-strated by the oxide-defined laser diodes of this Example, one of their more notable features was their simple fabrica-tion. Although a CVD SiOZ layer to mask to define the 10 um W0 92/12536 -35' PCT/US91/045I2 wide GaAs contact stripes was employed, elimination of "his step can be accomplished simply by photolithography, which would make possible the fabrication of an oxide stripe laser f ree of any CVD processes .

_.,._ w.~~,r~nr r.
TTA'1'_tVE O~:IDI:;-DF,FINED rItTLTIPLE STRIPL
A1 Ga, T~.~~-GaAs pUANTUT~! WEhL HETEROSTRUCTURE LFSERS
t -~- ;
ns demonstrated in Example 2, ttoe more notable faatures of the native AllGa1-xAs (x of about equal to or greater than U.7) oxide that. forms in accordance with the method of the present invention include how well it metal-7.ized, (thus employable in device heat sinking), and how, via ordinary photolithographic processes, the native o~:ide per-mitted delineation of device geometries without the need t.o deposit foreign anti potentially mismatched dielectric mater-ials (such as, Si02 or Si.~N4). The present E::ample amplifies these f eat.ures of the native ~~lXGa1-xAs ( x as def fined above ) oxide formed in accordance with the present invention by constructing, with simplified processing, high performance ten-stripe AlxGa~-XAs quantum-well heterostructure (QWH) lasers. The considerable difference in the oxidation behav-1 Or of A1 Ga., AS ( X Of a~7nt~t= a q~ta 1 t-O Or 7r oa tO.r t hail v . 7 ) X 1-X ' as compared to GaAs, which, relative to oxide formation, is much weaker and readily permits current-contact metalliza-tion, is shown.
The epitaxial layers for these coupled-stripe QWH
lasers were grown on n-type (100) GaAs substrates by metal-organic chemical vapor deposition (MOCVD) as described in the Dupuis, et al. reference cited in Example 1. A GaAs buffer layer was grown first, followed by an n-type A10,8Ga0,~As lower confining layer. The active region of the QWH was grown next and consisted of a GaAs quantum well (QW) having a thickness of about 400 R with A10,2JGa0,75As waveguide layers (undoped; having a thickness of about 1000 ~) on either side.

W0 92/12536 -~7- PCT/US91/04512 ~_,astly~, a: p-tY~?~ /;10. ~GaO. 2As upper confining layer was drown to a t2u:i.ckness of about 9000 k on top of the active region.
The entire nWH was capped by a heavily doped p-type GaAs contact layer about 80U A thick.
Tne GaAs contact layer was removed; where desired, to provide access to the upper confining layer for conversion of part of that layer to the native coxide by the method of the present invention. The GaAs contact layer did not oxi-dize readily, and consequently could be used directly as mask (and them contact layer) when the native oxide formed from a portion of the upper confining layer. Standard photo-lithography was used to mask sets of ten GaAs stripes, 5 um wide; located 2 pn apart (7 ~.m center-to-center spacing).
The GaAs between the stripes (2 um width), as well as the GaAs between sets of stripes, was removed with H~S04:H?02:H20 11:8:80). This exposed the high composition AlxGal-xAs (x, of about 0.8) upper confining layer to oxidation in accord with the present invention. The gWH was heated at 400°C for 3 hours in an H20 vapor atmosphere obtained by passing N2 car-rier gas (ha,Ji ng Q flow rate of about 1.4 scfh) through an HBO bubbler maintained at 95°C.
The QWH crystal after oxidai:ion is shown in Fig.
9(a). The 5 wn GaAs contact stripes i:emained shiny (silvery) and basically unaffected by the oxidat:ian. The remainder of the crystal, including the 2 um regions between the GaAs stripes, is covered with the native oxide tYrat formed by the method of the present invention. The native oxide was clear and transparent and uniform; it appeared blue in color be-cause of optical effects and was 1000-1500 A thick. The thickness of that portion of the upper confining that was converted to native oxide was also about 1000 - 5000 A. Thus the thickness of the native oxide was substantially the same WO 92/12536 ° 38-- PCT/US91/04512 as or ~.oas than the corresponding thickness of the aluminum-boar inc7 upper conf fining layer .
After the pWH was mctallized with titanium-plat.-inum-gold (Ti-Pt-Au) by conventional techniques, across its entire suz~facer it appeared as shown in Fig. 9(b). Before metallization occurred, the crystal was Zn diffused (ZnAs2, 540°C, 25 rain) to a shallow depth to improve the contact on the GaAs stripes. This procedure did not require and' special mashing. The crystal was thinned to about 100 dun and was metallized on the substrate side germanium-gold-nickel-gold (Ge-Au-Ni-Au), and cleaved into Fabry-Perot resonator strips that were t2ien saw-cut into separate 10-stripe dies. These were attached to copper (Cu) using indium (In) on the stripe side for heat sinl~>ing and electrical test. Died-~_ current versus voltage (I-V) characteristics had low series resis-tance (approximately 2 ohm, S2). This indicated that the GaAs contact la~~er was not affected by exposure to the oxidation method of the present invention. Additionally, the low leak-age currents showed that the native oxide provided good cur-l eii t i lOCkl.iicj .
The near-field and far-field radiation patterns of one of these devices are shown in Fig. 10. The device was mounted with the junction side upwards, and had a threshold of about 95 mA cw. Fig. 10(a) shows the near-field image as viewed with a Si metal oxide semiconductor (MOS) camera at a continuous wave (cw) laser current of 100 mA. Eight of the ten emitters of the array lased at this current. The other two stripes were visible on a more sensitive scale, but could not be shown without saturation of the camera by the eight more intense emitters. The near-field image, Fig. 10(a), demonstrates that effective current confinement is provided by the native-oxide-defined stripes.

icr. 1001 show:; the far-field pattern for the same device used, for Fig. 10(a): The radiation was collimated with a 25 mm f/0.95 lens and imaged on a l.~near charge-c:oupled device array. The twin-lobe ;pattern shown is char-acteristic of coupling with n-phase shift between emitters.
The lower trace of Fig. 10(:b) shows the far-field pattern at 100 mA cw that corresponds to the near-field pat-tern shown in Fig. 10(a). The left peak was dominant because of non-~,zniforrn current injection and non-uniform operation near the losing threshold. The peak ;separation of 6.8°
agrees with the calculated value of 6.9° for the 7um emitter spacing (with a wavelength of 8470 A),. The full angle at half-power (FAHP) of the left peak at 100 mA was 0,6°, which indicates that coupling across the fu7:1 68 tun aperture of the array (ten, 5 um wide stripes on 7 pn centers) occurred. At higher currents, the carrier injection and the emitter inten-sity were more uniform, resulting in t:he more balanced twin-lobed far-field pattern shown at 145 mA in Fig. 10(b). Both lobes of the top trace have a FAHP of 1.1°, indicating weaker coupling of the 3rra~~ and; or coupling across a reduced aper-ture of about 44 pn (7 emitters). The decreased peak separa-tion of 5.0° indicates a slightly smaller phase shift between emitters (the effect of transverse gain). An array of uncou-pled 5-~.un wide emitters would have a far-field divergence angle of 10° FAHP, roughly 10 times greater than the lobe widths of the coupled array demonstrated here.
Because of the simple form of these coupled-stripe lasers and how well they are heat sunk via the GaAs contact stripes and the recessed native oxide, they were capable of considerable power output before failure. The power versus current behavior (continuous wave at 300° K) of one of the diodes is shown in Fig. 11. The inset shows the output spec-WO 92/12536 a s -40- PCT/US91/04512 crum at i0 mw (one facet), which shifted from 8456 ~, (i.466 V) to a dominant. mode at 8479 A (1.462 eV) at higher drive currents and an output power of about 100 mw (single facet).
This corresponds to a temperature increase of about 10°C or less, when there is significant bandfilling.
Inasmuch as the gain-guided lasers of this Example couple over large distances, the emitter spacing can be fur-ther increased and the heat sinking further improved. Fig.
12 shows the power versus current behavior of a 20-stripe laser similar to that used in Fig. 11, but.,aith stripe separ-ation increased to 5 um (see the Fig. 12 inset). Because of power supply limitations, the laser operation was terminated at 400 mw (single facet; 2 amp. A).

r~: r ntnr r n tJATIVE OXIDE MASY;ED IMPURITY--INDUCED LAYER
DI SORDERING OF A1 ,Ga ,As QUANTUM 4rTELL HETEROSTR'JCTURES
This example investigated the masking capability of the native oxide tha forms on Al~Ga1_,XAs (X > 0.7) using the present invention. In particular this. Example contrasted Zn diffusion and impurity-induced layer disordering (IILD) be-havior between a bare AlhGa1_xAs-GaAs superlattice (SL) or quantum well heterostructure (QWH) crystal, and a SL or gWH
that was masked by a native oxide formed by the method of the present invention. In the latter case (native oxide masked) the quantum well (QW) and superlattice (SL) layers were shown to be preserved.
The superlattice (SL) and quantum well heterostruc-ture (QWH) crystals used in this Example were grown on (100) GaAs substrates by metalorganic chemical vapor deposition (MOCVD) as described in the Dupuis, et al, reference cited in $xa.mpl a 1 , In the case of tile JL trryJr tal ( crystal ~ i ) , a GaAs buffer layer was grown, followed by an undoped A10.8Ga0,2As lower confining layer (the thickness of which was approximately 0.1 dun) : Then the S:L, consisting of 40 GaAs wells (L" of about 110 A) and 41 ,~10.4Ga0,6As barriers (LB of about 150 A), was grown. The total SL thickness was approximately 1.05 tun. Lastly, a 1000 R A10,8Ga0.2As upper confining layer was grown on top of the SL. The structure was then capped with a 3000 A GaAs layer.
In the case of QWH crystal, i=he first part of the MOCVD QWH (Crystal # 2) was an n-type GaAs buffer layer (about 0.5 tun thick), which was followed by an n-type A10.~5Ga0,75As intermediate layer. An n-type A10,8Ga0.2As 209~g lower confining layer was grown next. This was followedhy flue pWli active region, which was a AlO,ObGaO.g~As (QW) quan-t171i1 wE'l1 about 200 ~ thick, sandwiched by two undoped A10 . Z,GaO , ~ JAs waveguide ( i~7G ) Layers of about 1000 n . Fin-ally a p-type F,10.8Ga0,2As upper confining layer was grown to a i_hickness of about 9000 h) on top of the active region.
The entire QWH, useful in laser diode construe+:.ion, was cap-ped by a heavily doped p--type GaAs contact layer havinq_ a thickness of about 800 A.
The GaAs cap layer. on both the SL and the QWH, was removed to expose the upper AIGaAs confining layer (x of about 0.8) to the oxidization method of the present inven-tion. The presence of Ga in the oxidized layer ar_d at the native oxide-semiconductor interface did not adversely affect the structure of the native oxide that formed because the oxygenated gallium and aluminum compounds form structural isomorphs having similar crystalline form, and A1203 and Ga2oj form a solid solution over the entire compositional range represented by the upper confining layers of the SL and ,.. ,.
vwri. The A~xGal-XAS nxirl~tiCn ;~;uS gC.:.Cmpii,Sh ed iii c'tCl:vrCl with the present invention by heating the samples at 400°C
for 3 hours in an ii20 vapor atmosphere obtained by passing N2 carrier gas (with a flow rate of about 1.5 scfh) through an H20 bubbler rna.intained at 95°C.
In order to effect selective Zn diffusion and layer disordering in the SL sample (Crystal #1), a photoresist stripe pattern (20 um stripes on 50 um centers) was defined on top of the native oxide thus formed. Using a NH4F:HF
(7:1) buffered HF solution, the native oxide was selectively removed in a stripe pattern, as shown in Fig. 13. The sample was then cleaned in an NF~40H solution and immediately sealed in an ampoule with a piece of ZnAs2 (lU mg) for the Zn diffu-WO 92/12536 ~ '1'1 ,11CT/US91 /04512 lion (at eU0°C for i hour). A shallow-angle lap of th~~ SL
sample after the diffusion is shown in: Fig. 13. The native oid~ mask, formed in accord with the practice of the present invention, which is indicated by the downward arrow labelled "oy.ide" in Fig. 13, masked the underlying A10.4Ga0.6As-GaAs SL from the diffusion of Zn, and from layer intermixing that occurred in areas where the oxide had been removed. The 40 period SL (having a total thickness of about 1:05 um) was seen to be clearly intact ber~eat.h the native oxide mask, while intermixed elsewhere.
In the case of the QWH wafer (Crystal #2), two sample; were sealed in an ampoule with ZnAs2 for simultaneous heating and for IILD diffusion (at 5?5°C for l hour). One sample had a native oxide maskina layer on it as formed by the method of the present invent~.on, while the other sample was the QWH with simply the GaAs cap layer removed. Similar to the selective Zn-IILD of the SL of Fig. 13, the QWH sample having the oxide as formed according to the present inven-tion, did not disorder. In comparison, layer intermixing occurred for tllP QWT_j Onmpari_cn_n_ g~~,n~ a :~:hiCh d' ~
r~ .i.~. nw iauvc we native oxide masking layer on it; (as determined shown by photoluminescence measurements).
The QWH samples, both masked and not-masked, were prepared for photoluminescence measurements by first lapping and polishing the crystals, using conventional techniques, to a thickness of approximately 2 mils. tJext, the remaining substrate and GaAs buffer material were removed by wet chemi-cal etching in H2S04:H202:H20 (4:1:1), followed by selective etching. A photomicrograph of an oxidE~-masked portion of the QWH (Crystal #2) is shown in Fig. 14. The photomicrograph of Fig. 14 was taken with light that was transmitted through the thinned QWH crystal at a spot which wa~~ "rough etched" all cI-rc: way to the oxide layer, thus revealing features or the QWH and o.f th~~ rrati ve oxide that was produced Ly . the me thod of the L>resent invention .
RefCL'I'ing to Fic~. 14, Region A of the photomicro-graph showed the native oxide to be of excellent quality, i.c., it was clear and transparent and similar to the oxide that was produced in the oxidation of l:he AlAs-GaAs SL cry-stals of Example 1. Indeed, the oxide was so clear that specks of dirt on thr~ surface of the oxide were easily seen.
~'ho remaining regions showed the various layers of the QWH
material deeper into the crystal. At Region B, the oxide plus the upper QWH confining layer (AlO.~Ga0.2As) were seen and were yellow in color, due to optical effects. In Regio:.
C, the waveguide plus the QW active region, as well as the upper and lower confining layers, were seen as or4nge in color, also due to optical effects. Finally, in Region D, the entire thickness of the QWH was seen as red in color (again due to optical effects). Some of the buffer layer (where X was about 0.25) that was not completely removed at t~"1!~ f_'YlIC'f'.~l edgy ;~;u~ ul.Sv jGeit Zn IlegZOn D.
To further examine the capability of the native oxide that is produced by the present invention to mask the crystal from Zn-IILD, cleaved samples were examined via photoluminescence (PL). Native-oxide masked and non-masked samples that had been exposed simultaneously to the Zn and As ambient at 5?~°C for 1 hour (the Zn-IILD) were heat sunk in copper under diamond for photopumping with an Are laser (5145 A). The resultant photoluminescence spectra (laser opera-tiore) are shown in Fig. 15.
Fig. 15(x) shows that the lasing wavelength (con-tinuous operation, 300° K) for the native-oxide-masked sam-ples occurred at 7992 A (1.565 eV); while that for the pulse-W0 92/ 12536 - 4 5 - PCT/US9l /04512 oxcited non-masked comparison samples, Fig. 15(b) was shifted to 7140 R (1.736 eV). The shift of approximately 170 meV in the: laser operation of the non-masked gWH crys al (Zn-ILLD), Fig . 15 ( b ) , agreed with what was expected f or a Aly Ga.l -};As QW
(x of ak~out 0.06) intermixed into a bulk-crystal waveguide region (x of about 0.25). This indicated that the non-masl~:ed samples had been intermixed ;(with an energy shift of about 170 meV), while the native-oyide-masked samples, Fig. 15(a), were intact. Also, for the Fig. 15(a) samples, QW band-fill-ing was evident, while for the IILD Fig. 15(b) samples, only x~ulk-crystal behavior was evident. Interestingly, photoexci-tation of the native-oxide-masked (a) samples of Fig, l5(a) t~or, place through the transparent oxide, indicating that the native oxide, formed by the present method was of high qual-ity.

WO 92/12536 ~ - '~ b - PCT/US91 /04512 i~XAT~1PLE
LOW-'THRESHOLD DISORDER-DEFINED 2dATIVE-OXIDE-DELINEATED
BURIED-FiETEROSTRUCTURE A1 Ga As-GaAs QttANTUI~g WELL LASERS
Impurity-induced layer disordering (IILD), such as described by W. D. Laidig, et al. in Appl Phys. Lett., _38, 776 (1981) and D. G. Deppe, et al. in J. Appl. Phys., 64, F.93, (1988), has been employed to produce very high per-formance planar buried-heterostructure (BH) quantum well heterostructure (QWi3) lasers such as described by D. G.
Deppe, et al. in J. Appl. Phys., 58, 4515 (1985). Various dopants and diffusion techniques have been employed to fabri-cate disorder-defined BH lasers, including: (1) Si solid-sourc~ diffusion, (2) Si implantation and annealing, (3) Ge diffusion from the vapor, (4) Zn diffusion from the vapor, (5) Si-O diffusion from A1-reduced Si02, (6) Si diffusion from Al-reduced Si/Si3N4 via rapid-thermal annealing, and (7) Si diffusion from laser melted Si.~t~4. Many of these diffu-sion sources and tecnniq~~es s~,~f~~Y ;r ~-h =_, ,_ 1 \.1 11 c»~ ~~ a ~ d~ t tmaL they form a very highly conductive layer at the crystal surface, possibly due to the formation of a dopant-crystal alloy.
This conducting layer is a source of leakage, thus increasing laser threshold currents. Indeed, under certain conditions, the dopant-crystal alloying i~ so severe that a relatively deep proton implant is required to passivate the leakage regions and ensure low threshold operation.
This Example demonstrates a "self-aligned" process, in which the crystal surfaces were converted to a high-quality, current-blocking native oxide by the method of the instant invention. The oxide thus formed was found to passi-vate the surface, thus reducing leakage currents and yielding an improved form of low thre hold disorder--defined BH
AlxGa1-xAs-GaAs quantum well heterostructure laser.
The QWH laser crystal employed in this Example was grown by metalor.ganic chemical vapor deposition (MOCVD), as described in the Dupuis, et. al. reference cited in Example 1, on an n-typo substrate. The growth b~_gan with n-type buffer layers of GaAs having a thickness of about 0.5 um and Alp , 25Ga0 , 75As having a. thickness of <~bout 1 dun. This was followed by the growth of: an approximately 1.1 um thick A10.77Ga0.23As n-type lower confining layer; an approximately 2000 R thick A1p,25Ga0.7~As undo~ed waveguide region; an ap-proximately l.1 um (11,600 P~) thick A10.8Gap,2As p-type upper confining layer; and an approximately 0.1 pn thick p-type GaAs cap. In the center of the waveguide, a A10.06Ga0.94As quantum well, undoped, having a thickness of about 20U R was grown.
The laser diode fabrication process began with a shallow Zn diffusion over the entire surface, in an evacuated quartz ampoule at 540°C for 30 min. The shallow p+ layer ;ormAd by the diff~,aicr. helped control. iaterai Si diffusion at the crystal surface (under the masls:ed regions) in later processing steps. After Zn diffusion, the crystal was encap-sulated wi h about 1000 A of Si3NQ which was deposited by conventional chemical vapor deposition (CVD) at 720°C. The Si3N4 was patterned with photoresist a.nd etched with a CF4 plasma into two stripe widths: 4 pn a.nd 6 um: The photo-resist was removed, with the remaining Si3N~ stripes serving as masks during chemical-etching, with H2S04:H202:H20 (1:8:80), of the GaAs contact layer. This etching left the high-gap A10,8Ga0.2As upper confining layer exposed. Follow-ing stripe delineation, CVD techniques were used to deposit an approximately 300 A thick Si layer (CVD at 550°C) and an W0 92/ 12536 - ' 8 - PCT/US91 /04512 approximately 1700 A thick Si02 cap layer (CVD at 400°C).
The crystal was the~t'.sealed in an evacuated quartz ampoule and annealed with excess As at 850°C for 6.5 hours. The high temperature anneal resulted in Si diffusion and IILD outside o.f the GaAs contact stripes.
The encapsulant was removed by etching with a CF4 plasma, and the crystal was oxidized according to the present invention as follows: The crystal was placed in an open-tube furnace (supplied with a N2 carrier gas bubbled through HZO
at 95°C) at 400°C for 3 hours. This resulted in the conver-sion of approximately 2000 A of the exposed upper confining layer at the edge and beyond the GaAs contact stripe regions.
The thickness of oxide layer formed was s~.tbstantially the same as the thic?mess of tha t portion of the upper conf fining layer that was converted. No oxide was formed on the GaAs contact stripes due to the selectively of the oxidation pro-cess. The formation of native oxide only in areas of high aluminum composition resulted in contact stripes that were seJ.f-aligned. Following oxidation by the method of the in-vention, the wafer was sealed in a.~. a.Tp~vuic wit h d GilA~2 source, and was annealed at 540°C for 30 min to form, only in the contact areas, a shallow, heavily doped p-type region.
Samples were then conventionally lapped to a thickness of about 5 mils, polished, metallized with titanium-gold (Ti-Au) on the p-type side, metallized with germanium-nickel-gold (Ge-Ni-Au) on the n-type side; the samples were then cleaved into bars approximately 250 lun in length.
Figure 16 shows a scanning electron microscope SF.M) image of a stained cross section of a 6-Wn-stripe BH
laser structure after the Si-IILD and the oxidation method of the present invention that resulted in self-aligned con-tact stripes. Reference to Figure 16 shows that the impur-2~r~~~8~
qty-induced layer disordering intermixed the waveguide region with the surrounding confining layers (autside of the GaAs contact region) and provided current ~,~.onfining p-n junctions.
Lateral diffusion resulted in a contact region of appro;:i-mately 5.5 dun and an active region having a width of approxi-mately 7 um. Similarly, for diodes processed with 4 l.~m stripes, the contact region was about 2..5 l.un with an approxi-mately 3pn wide active region. Oxidation by the method of the present invention, of'the high-gap AlxGalOxAs regions outside of the GaAs contact stripe resulted in the formation of a high-quality current-blocking native oxide at the cry-stal surface. The oxide grew all the way to the edge of the GaAs contact stripe, a indicated in F'ig. 16 by the unmarked vertical arrows at the "notch" at the stripe edges. This resulted in the self-aligned passivation of areas having the potential for leakage by conversion of these areas to the native.oxide. The native oxide was actually thicker than it appeared in Fig. l6 since the stain, Y,3Fe(CN)6-KOH, that was employed to resolve the heterolayers also etched the oxide.
Th°_ laser diodes fabricated using native oxide as formed by the present invention typically exhibited pulsed thresholds between 3.5 mA and 6 mA (for the 3 pn stripe) and 7.5 and 9.5 mA (for the 7 ~ stripe), ,as tested in a probe station. Figure 27 shows the continuous wave (cw) light power versus current (L-I) curve of a :3 Wn stri.pe diode that was mounted p-side down on an indium-coated (In-coated) cop-per (Cu) heatsink. The room temperature (300° K) continuous wave (cw)) threshold was 5 mA for this device (uncoated fac-ets). Spectral data indicated that the: diode first began to narrow spectrally and "ring" at about ~~ mA, which accords . with good carrier and optical confinement and low edge leak age. Lasing occurred at $198 R, with single-longitudinal WO 92/ 12536 ~~ 5~ ~~ PCT/LJS91 /04512 _..
node operat.i.~n well developed at ? mA and extending up to at least 20 mA. The laser diode exhibited an external differen-tial quantum efficiency of 53~ (up to about 10 mW) and an output power of greater than 31 mW/facet before catastrophic damage occurred. At powers e~reater than 10 mW, the increas-ing curvature of the L-I plot indicated that heating effects becarne significant. However, this phenomenon was due to the relatively high forward resistance of the diodes (R~ of about 20R), and not. to the inability of the native oxide to dissi-pate heat. Thus the native oxide formed by the method of the instant invention acted as an excellent current-bloc);ing layer for stripe-geometry laser diode operation. These diodes exhibited sharp turn-ons and no observable leakage through the oxide. ' Unmounted, the laser diode of Fig. 17 exhibited a pulsed threshold of 4.5 mA. Other diodes also exhibited a very small increase (usually less than 0.5 mA) in pulsed (unmounted) versus continuous wave (mounted) laser thres-holds. These increases were much smaller than those typic-ally observed for other fabrication processes. This was attributed to better thermal contact between the metalliza-tion and the oxide formed by the invention, as well as better oxide heat conduction, over that for other masking encap-sulants. In addition, the formation of the native oxide by the invention "consumed" the highly doped surface layer.
Thus, the high-gap shunt junctions had lower doping, and thus lower capacitance. Compared to continuous wave operation, high shunt junction capacitance causes the leading edge of a pulsed current to divide differently between the quantum well junction and the shunt IILD junction, which leads to a sig-nificant difference in pulsed versus continuous wave laser thresholds. Thus diodes with lower shunt capacitances will WO 92/12536 - ~' ~ - '~ ~ ~ ~ ~ PCT/US91/04512 hrive more similar pulsed and continuous wave laser thresholds than those with high capacitances.
The ~:ield pattern:: of a 3-u,m stripe laser are shown in Fig. 18 for continuous wave operation at 12 mA. The tiear-field pattern, Fig. 18(a), had a full width at half maximum of about 3.~u,m, which agreed closely with an active region having a width of about 3 um, as observed in SEM micrographs.
The far-field pattern, Fig. 18(b) had a full angle at half maximum of about 20 . 4 ° , wh.ich corresponded to the dif f racoon limited operation of a 3 um stripe.

W0 92/ 12536 ' 2 PCT/US91 /04512 EXAi~IPLE 6 Np.TIVE OXIDE STAF3ILIZATION
OF AlAs-GaAs HETEROSTRUCTURES
This Example compares the high quality and stabil-izing nature of the native oxide formed in accordance with the present invention with the inferior quality and destruc-tive nature of oxides that form at temperatures lower than that prescribed in the practice of the instant invention. In particular, this Example compares the quality of the native oxide that forms on ex>posure to water vapor and nitrogen gas and a temperature of 400°C after 3 hours, with the oxides) that form by exposure to atmospheric moisture and tempera-ture, which conditions are representative of oxide formation under a temperature of 375°C.
The crystals used in this experiment were grown by metalorganic chemical vapor deposition (MOCVD) on (100) n-type GaAs substrates in an EMCORE GS 3000 DFM reactor at 760°C. The crysta_1 gro~~tr prossurc, Group V/Grc~up iii ratio, and growth rate were 100 Torr, 60, and about 1000 A/min, respectively. An undoped GaAs layer approximately 0.5 dun thick was grown first, followed by an nominally undoped AlAs layer about 0.1 iun thick. The crystal was then cleaved in two. One half of the cleaved crystal was exposed to atmos-pheric conditions at room temperature (Sample a). The other half was oxidized, according to the method of the present invention, at a temperature of 400°C for 3 hours in an H20 vapor atmosphere obtained by passing N2 carrier gas (having a flow rate of about 1.5 scfh) through an H20 bubbler main-tained at 95°C (Sample b). Sample (b) was then exposed to atmospheric conditions identical to those for Sample (a).

i;
WO 92/ 12536 - ~' ~ - PCT/US91 /04512 ,,2~W6~ . .
within hours after exposure, the Sample (a) crystal began to degrade in color to a yellowish brown, while the Sample (b) crystal maintained a uniform blue: appearance (the oxide was clear and transparent, the blue color was a result of optical effects). Figure l9 is a t~lomarski image photo-graph of the surfaces of crystal Samp:Les (a) and (b) after, in both cases, atmospheric exposure for 100 days. The sur-face of Sample (a) was clearly "rougher" than that of Sample (b). Several days after the 100 day aging process, Sample (a) showed si_qns of nonuniformity around the edges of the crystal, while Sample (b) remained unchanged. The oxidized surface of Sample (b) was smoother than the surface of Sample (a), and the cleaved edge of Sample (b) was intact whereas the edge of Sample (a) showed signs of destructive attack (as indicated by roughening).
Figure 20 is a scanning electron microscope (SEM) image of the edges of Samples (a) and (b): The edges were unstained, cleaved cross sections that had been aged 100 days. Sample (a) showed signs of chemical attack into the Crystal. WhlCh dE'_pt~'1 waS well beyond thL' 3pproiii~?~atel;y U.1 /1m thick AlAs top layer of the As-grown crystal. In contrast, the cross section of the Sample (b) exhibited a native oxide layer that was substantially the same thickness as the AlAs top layer of the As-grown crystal, the thickness of the na-tive oxide being approximately 0.1 dun thick; the native oxide also showed no perceptible sign of degradation. The cross section of Sample (a) also appeared to be nonuniformly etched. This was surprising in that the sample was not stained to high-light this layer.
The results of secondary ion mass spectrometer (SIMS) analysis on Samples (a) and (b) talten after 80 days are shown in Fig. 21. Both Samples (a;l and (b) had large _ .- . _ WO 92/12536 ~~ t PCT/US91/04512 ~~ ~ , oxygen and hydrogen signals (indicated by J,l-O-H ion count) ire the top 0.1 lun of thickness. I~lore unusual was that Sample (a) showed a significant Al-O-H ion count as deep as about 1.0 um intc., the crystal itself. This was in sharp contrast to the A1-U-H signal in the Sample (b), where the ion count for A1-O-H decreased steadily after approximately the first 0.1 um of thickness, which represents the layer formed by the native oxide. The A1-U ion count tracked the x.l-O-H signal in bath samples. Another striking difference in the two crystals was the Ga depletion that was evident in the top 1 ~.m of Sample (a), which indicated that chemical reactions and degradation of the crystal was occurring. The Ga signal of Sa,~nple (a) increased at the AlAs-GaAs interface, that is, at approximately 0.1 dun, and then decreased again at the sur-face; however, no such "spike" in the Ga signal was observed in the case of the Sample (b) and Sample (b) did not show signs of any such chemical reactions or degradation; these results are in accord with the SEM images of Fig. 20 and demonstrate that the native oxide that formed from approxi-mately the first 0.1 Wn of Sample (b) by tho rnoth~d of the present invention was stabilizing in nature.
SIMS analysis also showed a dip in tire Al-O-H
signal in about the first 0.1 Iun of Sample (b) which dip was not present in Sample (a). Transmission electron microscope images of similarly oxidized heterostructures indicated that there was a slight contraction of the native oxide layer to roughly 60o to 700 of original thickness of the AlAs tap layer. This contraction can be explained by the fact that the molar volume of AlO(OH), which is one of the possible products of an A1-H20 reaction, and does not deleteriously effect oxide quality when present in modest quantities, is 270 less than the molar volume of AlAs. (The molar volumes WO 92/ 12536 ~' S 5" PCT/US91 /04512 of the anhydrous; a and phases of A12U3 are approximately oqual to that of AlAs which indicates formation of one or bath probably a-A1?O, as a major component of the native oxide of the instant invention). The contraction of the AlAs layer to about 0. 06 Wn to 0 . 0-I dun ( as indicated by the dip in the T.1-O-H signal) suggests that A10(OH) is either an inter-m~diate or, less likely, an end product of the oxidation method of the presen'~ invention. I~lore likely, the contrac-tlUll lIl thicYness is caused by the loss of arsenic. Several reactions involved in the AlAs oxidation are possible:
AlAs + 3Y.20-~ A1 ( OH ) 3 + AsH3 ~ ( 1 ) AlAs i 2H20-~.3A10(OH) + AsH3 '~ (2) ;Alms + 3H20 -~ Al?03 + 2AsH~ ~ (3) Reactions involving the formation of As20.1 are also possible but are less likely given the extent of As depletion (as shown in Fig. 21) in the AlAs layers in both the Samples (a) and (b).
Reaction (1) probably occurs in Sample (a) and is likely responsible for the inferior quality of the oxides) produced; the standard heat of formation of A1(OH)3 being greater than that of either a-A1203, ~ -Al2o.~ or A10(OH) at 300°1:. This is also in agreement with the phase diagrams showing the most thermodynamically stable phase at 300°K
under atmospheric pressure. See, E. M. Levin, et al. Phase Diagrams For Ceramists (The American Ceramics Society, Colum-bus, Ohio) Fig. 2008, P. 551 (1964); Fig. 1927, P. 527 (1964) and Fig. 4984, P. 426 (1975).
The As depletion that occurs in roughly the first 0.1 um of Sample (b), as shown in Fig. 21, was two orders of WO 92/ 12536 - ' ~ - PCT/US91 /04512 magnitude greater than that for Sample (a). This suggests ll~at a second reaction irf the AlAs layer of Sample (b) takes pl.acA which liberates still more As (as the volatile product A~fl3) thus increasing contraction of the native oxide layer.
The possible reaction may be:
A10(OH) + AlAs + H20 -~ A1203 + AsH3 '~' (4) The greater As depletion in the AlAs layer of Sample (b), as cotnpared to Sample (a), indicates that As may play a signif-icant role in the formation of the stable native oxide of the invention and may, in fact, catalyze the reaction of hydroxyl (OH ) groups in AlAs. The presence of hydroxyl groups are thought to be responsible for the instability of the oxides of Sample (a) and for the inadequacies of oxides from prior art thermal oxidation techniques.
As to oxygenated gallium compounds, gallium tri-hydroxide, Ga(OH).~, is the most likely Ga-O-H compound formed at room temperature and atmospheric pressure. Gallium hy-droxyoxicie, Ga0(OH), is the most likely form at about 100°C
and gallium oxide, a-Ga203, the stablest form, at about 400°C. Both Ga(OH)3 and Ga0(OH) have inadequate physicality for semiconductor purposes and also would cause an expansion in oxide thickness when present. It is believed that Ga(OH)3 and Ga0(OHj are formed at temperatures under the 375°C pre-scribed by the practice of the present invention and thus would likely be formed in undesirable quantities by thermal oxidation techniques of the prior art. Because Ga(OH)3 is a much stronger acid than is A1(OH)3, A1(OH)3 being amphipro-tic, there is also a strong likelihood that a reaction be-tween these two hydroxides occurs thus further exacerbating the deleterious effects these materials have on semiconductor structure. Since (when in hydrous form) both are also elec-WO 92/12536 r~7 PCT/US91/04512 trc~lytos, the presence of light may contribute to the re-action .
~dh;lc~ there are indications that Ga-O-H and AI-O-H
compounds are also present in the native oxide of the present invention it is clear that even if prE:sent, they did not at-tach tree crystal of Samplo (b) as in t:he case of the Sample la). The reduction of these particular hydroxides at higher temperatures used in forming the native oxide of the present invention (at greater than about 375°C:), apparently stabil-izes the A1-H2o and Ga-H20 reactions; thus inhibiting the destructive chemical reactions attendant lower temperature oxidation.

WO 92/12536 -S~' PCT/US91/04512 T~Y1~.~.TT~T L' '1 FATE OF r:ATTVE OXIDi~'~', FORI~'IATION B'.~' RAPID THERIdAL PROCESSING
J'. f urnance at 650°C was ~;rovicied with a water vapor environment obtained by passing N2 gas through an H20 bubbler at 95° w 10~°C; nitrogen gas flow rate was appro~;imately 1.9 scfh.
Zn order to minimize thermal mass effects, the quartz boat used to carry the samples of this example remained in the furnace until the samples were ready to be oxidized. The samples utilized were a crystal having an AlvGa1'Yt,s layer, where x was between about 0.8 to about 0.9.
To oxidize the crystals, the quartz boat was removed from the furnace and a sample was loaded onto the boat. The sample and boat were then placed into the furnace.
Oxidation time periods of between about 15 seconds to about l0 minutes were employed for separate samples. At the end of each oxidation the sample used was quickly removed from the fur nace .
For each sample, the rate of native oxide formation was observed to be about 0.1 Iun (about 1000 A? of native oxide formed for about every 15 seconds of oxidation time using the rapid thermal processing of the present invention.

W0 92/ 12536 "' 9 - PCT/US91 /04512 _-.~~w,T r. ~t ItJDEX OF REFR/~CTION MEASUREMENTS
A native oxide layer was formed from four samples of A10,8Ga0.lAs (each such layer was about 0.4 um thick) overlaid on a GaAs substrate. The samples, Samples l-4, each had a GaAs cap (about 0.1 ~.un thick) which was removed with an ~I2SOQ:H202:H20 (1:8:80) solution; the samples were immediately oxidized in accordance with the procedure used in Example 7. Oxidation times for Samples 1-4 were 1, 2, 4 and minutes, respectively.
Eliipsometer measurements, using conventional equipment and a wavelength of ~~ = 632'r3 R, determined the thicl~:ness and index of refraction of 'the oxide layers thus formed in accordance with the present invention. The results are shown in Table 2, below:
TABLE ?.
Oxidation Index of Sample Time (min. Thickness (dun) Refraction (n) ) 1 1 0.38 1.57 2 ?. 0.41 1.54 3 4 0.39 1.55 4 10* -- --* Data for the 10 minute oxidation time are not presented due to significant scattering of the probe beam which reduced the accuracy of t2ne measurements.

WO 92/12536 ~ ~ ~ ~ f ~ PCT/L,'S91/04512 As aYpar<°nt from Table 2, the Alp~~Gap.lAs layers Samples 1-3 were ~substanti.ally completely oxidized and that.
the thickness of the resulting native oxides were :substantially the same as or less than the thicl~:ness of the Al~~BGa~~.iAs layers that converted. The indices of rc.f.raction of the native oxides thus formed ranged from 1.54 - 1.57, which indicated that the native oxide thus formed on each sample was formed primarily of dehydrated aluminum compounds .

Claims

What is Claimed is:

1. A method of forming a native oxide from an aluminum-bearing Group III-V semiconductor material which comprises exposing an aluminum-bearing Group III-V semi-conductor material to a water-containing environment and a temperature of at least about 375°C to convert at least a portion of said aluminum-bearing Group III-V semiconductor material to a native oxide characterized in that the thick-ness of said native oxide is substantially the same as or less than the thickness of that portion of said aluminum-bearing Group III-V semiconductor material thus converted.
2. The method of Claim 1 wherein the thickness of said native oxide is between about 0.6 to about 1.1 times the thickness of said aluminum-bearing Group III-V semiconductor material thus converted.
3. The method of Claim 2 wherein the thickness of said native oxide is about 0.7 to about 1.0 times the thick-ness of said aluminum-bearing Group III-V semiconductor mate-rial thus converted.
4. The method of Claim 3 wherein the thickness of said native oxide is about 0.8 to about 0.95 times the thick-ness of said aluminum-bearing Group III-V semiconductor ma-terial thus converted.
5. The method of Claim 4 wherein the thickness of said native oxide is about 0.85 to about 0.9 times the thick-ness of said aluminum-bearing Group III-V semiconductor ma-terial thus converted.
6. The method of Claim 1 wherein said water-con taining environment comprises water vapor and an inert gas.
7. The method of Claim 6 wherein said water-con taining environment comprises nitrogen gas substantially saturated with water vapor.

8. The method of Claim 7 wherein said nitrogen has a flow rate of at least about 0.5 standard cubic feet per hour.

9. The method of Claim 8 wherein said flow rate is about 1.0 to about 2.0 standard cubic feet per hour.

10. The method of Claim 1 wherein said temperature is about 375°C to about 600°C.

11. The method of Claim 10 wherein said temperature is about 390°C to about 500°C.

12. The method of Claim 11 wherein said temperature is about 400°C to about 450°C.

13. The method of Claim 10 wherein said exposing of said aluminum-bearing Group III-V semiconductor material to said water-containing environment and said temperature is for a time of about 0.1 hour to about 6.0 hours.

14. The method of Claim 13 wherein said time is about 0.1 hour to about 5.0 hours.

15. The method of claim 14 wherein said time is about 2.0 to about 4.0 hours.

16. The method of Claim 15 wherein said time is about 3.0 hours.

17. The method of Claim 1 wherein said temperature is in the range of over about 600°C to about 1100°C.

18. The method of Claim 17 wherein said temperature is about 650°C to about 1000°C.

19. The method of Claim 28 wherein said temperature is about 700°C to about 900°C.

20. The method of Claim 19 wherein said temperature is about 800°C.

21. The method of Claim 17 wherein said exposing of said aluminum-bearing Group III-V semiconductor material to said water-containing environment and said temperature is for a time of up to about 120 seconds.

22. The method of Claim 21 wherein said time is about 5 seconds to about 90 seconds.

23. The method of Claim 22 wherein said time is about 10 seconds to about 60 seconds.

24. The method of Claim 23 wherein said time is about 15 to about 30 seconds.

25. The method of Claim 1 wherein the native oxide is substantially free of hydrated aluminum compounds.

26. The method of Claim 1 wherein the native oxide is comprised primarily of dehydrated aluminum compounds.

27. The method of Claim 26 wherein at least one said dehydrated aluminum compounds is a-Al2O3.

28. The method of Claim 26 wherein at least one said dehydrated aluminum compounds is diaspore.

29. The method of Claim 1 wherein said native oxide is substantially free of aluminum suboxides.

30. The method of Claim 25 wherein said hydrated aluminum compounds include Al2O3 ~ 3H2O and Al2O3 ~ H2O.

31. The method of Claim 29 wherein said aluminum suboxides include ~-Al2O3, ~-Al2O3, ~-Al2O3, ~-Al2O3, ~-Al2O3, ~-Al2O3.

32. The method of Claim 1 wherein said aluminum-bearing Group III-V semiconductor material has the formula AlGaAs, AlInP, AlGaP, AlGaAsP, AlGaAsSb, InAlGaP or InAlGaAs.

33. The method of Claim 1 wherein said native oxide is substantially clear and transparent.

34. The method of Claim l wherein said aluminum-bearing Group III-V semiconductor material is overlaid on a surface of aluminum-free Group III-v semiconductor substrate.

35. The method of Claim 34 wherein said conversion of said overlaid aluminum-bearing Group III-V semiconductor material to said native oxide substantially terminates at the surface of said aluminum-free Group III-V semiconductor sub-strate.

36. A method of firming a native oxide from Al x Ga 1-x As wherein x is about 0.7 or greater which comprises exposing an Al x Ga 1-x As semiconductor material wherein x is about 0.7 or greater to an atmosphere of nitrogen and water vapor and a temperature of between about 400° to about 450°C
to convert at least a portion of said semiconductor material to a native oxide having a thickness substantially the same as or less than the thickness of that portion of said Al x Ga 1-x As semiconductor material thus converted.

37. The method of Claim 36 wherein said nitrogen is substantially saturated with said water vapor and has a flow rate of between about 1.0 to about 3.0 standard cubic feet per hour.

38. The method of Claim 36 wherein said exposure is for a time period of about 3.0 hours.

39. The method of Claim 36 wherein said native oxide is comprised primarily of dehydrated aluminum compounds.

40. A method of forming a native oxide from Al x Ga 1-x As wherein x is about 0.7 or greater which comprises exposing an Al x Ga 1-x As semiconductor material wherein x is about 0.7 or greater to an atmosphere of nitrogen and water vapor and a temperature in the range of over about 600°C to about 1100°C for a time period of up to about 60 seconds to convert at least a portion of said semiconductor material to a native oxide having a thickness substantially the same as or less than the thickness of that portion of said Al x Ga 1-x As semiconductor material thus converted.

41. The method of Claim 40 wherein said nitrogen is substantially saturated with water vapor and has a flow rate of between about 1.0 to about 3.0 standard cubic feet per hour.

42. The method of Claim 40 wherein said time period is about 15 to about 30 seconds.

43. The method of Claim 40 wherein said native oxide is comprised primarily of dehydrated aluminum compounds.

44. A semiconductor device comprising a native oxide formed from an aluminum-bearing Group III-V semiconduc-tor material by exposing said aluminum-bearing Group III-V
semiconductor material to a water-containing environment and a temperature of at least about 375°C to convert at least a portion of said aluminum-bearing Group III-V semiconductor material to said native oxide characterized in that the thickness of said native oxide is substantially the same as or less than thickness of that portion of said aluminum-bearing Group III-V semiconductor material thus converted.

45. The semiconductor device of Claim 44 wherein said device is an active device.

45. The semiconductor device of Claim 45 wherein said device is an optoelectrical device.

47. The semiconductor device of Claim 46 wherein said optoelectrical device is a laser.

48. The semiconductor device of Claim 45 wherein said device is a capacitor.

49. The semiconductor device of Claim 45 wherein said device is a transistor.

50. The semiconductor device of Claim 46 wherein said device is a waveguide.

51. The semiconductor device of Claim 47 wherein said laser has a ridged waveguide.

52. The semiconductor device of Claim 47 wherein said laser has a single stripe configuration.

53. The semiconductor device of Claim 47 wherein said laser has a multiple stripe configuration.

54. The semiconductor device of Claim 47 wherein said laser is configured as a surface emitter.

55. The semiconductor device of Claim 49 wherein said temperature is in the range of over about 600°C to about 1100°C.

56. The semiconductor device of Claim 55 wherein said composing is for a time of about 15 seconds to about 30 seconds.

57. The semiconductor device of Claim 55 wherein said device is a transistor.

58. A semiconductor laser which comprises:
a semiconductor substrate layer;
a first confining layer on said substrate layer;
an active region on said first confining layer;
a second confining layer on said active region;
said second confining layer comprised of a first aluminum-bearing Group III-V semiconductor material; and a current blocking layer on said second confining layer, said current blocking layer comprising a native oxide formed by the method of exposing at least part of the surface of said second confining layer to a water-containing environ-ment and a temperature of at least about 375°C for a time sufficient to convert at least a portion of said second con-fining layer to said native oxide characterized in that the thickness of said native oxide layer is substantially the same as or less than the thickness of that portion of said second confining layer thus converted.

59. The semiconductor laser of Claim 58 wherein said substrate layer comprises an aluminum-free Group III-V
semiconductor material, said first confining layer comprises a second aluminum-bearing Group III-V semiconductor material, said active region comprises at least two waveguide layers of a third aluminum-bearing Group III-V semiconductor material and a quantum well heterostructure disposed between said waveguide layers said quantum well heterostructure comprising a fourth aluminum-bearing Group III-V semiconductor material.

60. The semiconductor laser of Claim 58 further comprising a contact layer disposed intermittently on the surface of said second confining layer at areas of said sec-ond confining layer not converted to said native oxide.

61. The semiconductor laser of Claim 60 wherein said contact layer is intermittently disposed in a single stripe configuration.

62. The semiconductor user of Claim 60 wherein said contact layer is intermittently disposed in a multiple stripe configuration.

63. A diffusion mask for a semiconductor material comprising a native oxide formed by exposing an aluminum-bearing Group III-V semiconductor material to a water-con-taining environment and a temperature of at least 375°C to convert at least a portion of said aluminum-bearing Group III-V semiconductor material to said native oxide character-ized in that the thickness of said native oxide is substan-tially the same as or less than the thickness of that portion of said aluminum-bearing Group III-V semiconductor material thus converted.

64. The diffusion mask of claim 63 wherein said mask is effective against diffusion by zinc or silicon.

65. A native oxide formed from an aluminum-bearing Group III-V semiconductor material said native oxide being formed by a method which comprises exposing an aluminum-bearing Group III-V semiconductor material to a water-con-taining atmosphere and a temperature of at least 375°C to convert at least a portion of said aluminum-bearing Group III-V semiconductor material to said native oxide, said na-tive oxide characterized by a thickness substantially the same as or less than than portion of said aluminum-bearing Group III-V material thus converted to said native oxide.

66. The native oxide of Claim 65 where said native oxide is comprised primarily of dehydrated aluminum compounds.

67. The native oxide of Claim 66 wherein said native oxide is substantially free of hydrated aluminum compounds.

68. The native of Claim 66 wherein said dehydrated aluminum compounds include .alpha.-Al2O3 and diaspore.

69. The native oxide of Claim 66 wherein said tem-perature is in the range of over about 600°C to about 1100°C.

70. The native oxide of Claim 69 wherein said ex-posing is for a time of about 15 seconds to about 30 seconds.

71. The method of Claim 1 further comprising drying said native oxide in the absence of water.

72. The method of Claim 71 wherein said drying is in dry inert gas.

73. The method of Claim 72 wherein said inert gas is dry nitrogen.

74. The method of Claim 72 wherein said drying is at a temperature range of between about 375°C and 500°C.

75. The method of Claim 74 wherein said temperature range is between about 400°C and 450°C.

76. The method of Claim 71 wherein said drying is performed after exposing said aluminum-bearing Group III-V
semiconductor material to said water-containing environment and said temperature of at least about 375°C for a time per-iod of about 0.25 hour.

77. The method of Claim 76 wherein said drying is for a time of about 2 hours.

78. The method of Claim 1 further comprising annealing said native oxide.

79. The method of Claim 78 wherein said native oxide is sealed in an ampoule.

80. The method of Claim 79 wherein said ampoule has an overpressure of arsenic.

81. The method of Claim 80 wherein said ampoule has an overpressure of phosphorous.

82. The method of Claim 78 wherein said annealing is in the absence of water and is at a temperature in the range of between about 600°C to about 850°C.

83. The method of Claim 82 wherein said temperature is about 850°C.

84. The method of Claim 78 wherein said annealing is for a time period of about 0.25 hour to about 4 hours.

85. The method of Claim 74 wherein said drying temperature is ramped upward within said range of between about 375°C to about 500°C.

86. The method of Claim 74 wherein said drying temperature is ramped downward within said range of between about 375°C to about 500°C.

87. The method of Claim 82 wherein said annealing temperature is camped upward within said range of between about 600°C to about 850°C.

88. The method of Claim 82 wherein said annealing temperature is ramped downward within said range of between about 600°C to about 850°C.

89. The semiconductor device of Claim 46 wherein said temperature device has a first quantum well located within a second quantum well.

90. The semiconductor device of Claim 89 wherein said first quantum well is comprised of InGaAs and said sec-ond quantum well is comprised of GaAs.

91. The method of Claim 1 wherein said temperature is ramped upward from at least about 375°C during the expos-ing of said aluminum-bearing Group III-V semiconductor ma-terial to said water-containing environment.

92. The method of Claim 91 wherein said temperature is ramped upward from at least 375°C to about 600°C and said exposing is for a time of about 2 to about 4 hours.

93. The method of Claim 91 wherein said temperature is camped upward from over about 600°C to about 1100°C and said exposing is for a time of about 15 seconds to about 30 seconds.

94. The method of Claim i7 further comprising heating said aluminum-bearing Group III-V semiconductor material to said temperature in a heating time of about 2 seconds or less.

95. The method of Claim 94 wherein said heating time is about 1 second or less.

96. The method of Claim 94 wherein said heating starts at about room temperature.

97. The method of Claim 17 wherein said native oxide forms at a rate of about 0.1 µm for about every 15 seconds of said exposing.

98. The native oxide of Claim 65 wherein said native oxide has an index of refraction at .lambda. = 6328 .ANG. of less than about 2Ø

99. The native oxide of Claim 98 wherein said index of refraction is between about 1.54 to about 1.57.