DE3411191A1 - SEMICONDUCTOR ARRANGEMENT FOR GENERATING ELECTROMAGNETIC RADIATION - Google Patents

Description

PHN 10.639

"Semiconductor arrangement for generating electromagnetic ο ζ χ-οί U

The invention is directed to a semiconductor device for generating electromagnetic radiation in an active region of a first semiconductor material, Matrix material which is provided with a second semiconductor material in a structured manner.

A semiconductor device of this type is from the International (POT) published on November 11, 1982 Patent application ¥ 082-03946 known.

Semiconductor teranordniir ^ rT ¹ ~ i. :: n Err'vu.'ysn. ίΐ ikcrcnas ¹ -netic radiation are used in several areas of technology. They can be divided into arrangements whose radiation is not coherent and those whose emitted radiation is coherent. In the first case one usually speaks of LEDs ("Light Emitting Diode") in the latter package of lasers. The wavelength of the emitted radiation can be in the visible range of the spectrum, but also, for example, in the IR or UV range.

The radiation generated by known semiconductor lasers has a wavelength of 800 (in air) to 900 nm. It is desirable to use lasers for several reasons that emit radiation with a shorter wavelength. This is the case for example when storing information in video and sound carriers (VLP, DOR, compact disc) the required surface area for just one bit of information the square of the wavelength of the laser radiation is reversed proportional. Halving this wavelength offers the possibility of quadrupling the information density. An additional advantage is that a simpler optics is sufficient for shorter wavelengths.

A practical embodiment of an LED that emits green light is known from the article "An Experimental Study of High Efficiency GaP: N Green-Light-

PHN 10,639 ? 1-3-1984

Emitting Diodes ", published in RCA Review, HeTt 33, Sept. 1972, pp. 5I7-526. LEDs are described in it, whose diode is formed by monocrystalline semiconductor material, for example gallium phosphide, with heterojunctions between gallium phosphide and aluminum — gallium phosphide be formed, wherein the gallium phosphide can be p and η-conductive.

To increase the quantum yield of such LEDs, the gallium phosphide is doped with nitrogen.

It turns out that the quatene yield increases up to a certain level with nitrogen pollution. However, too large an amount of nitrogen leads to Lattice deformation in the gallium phosphide due to complex formation and thus to a reduction in the quantum yield.

In addition, there is nitrogen, which continues from the pn junction away, strongly absorb the radiation, so that the amount of radiation actually emitted decreases even further. Dissolving nitrogen in gallium phosphide up to the solubility limit is therefore not advisable.

In the already mentioned PTC application ¥ 082-03946, a laser structure is described in which the active area consists of a relatively large number of active layers of a semiconductor material with a direct band gap such as gallium arsenide, which are sandwiched between barrier layers made of semiconductor material with an indirect band gap such as aluminum arsenide and are separated from each other by them. These active layers and barrier layers together form what is known as a superlattice, which has an effective band gap between that of GaAs (1.35 ^eV ) and AlAs (2.30 eV), namely 1.57 eV, so that the radiation generated has a significantly shorter wavelength than would be the case if an active layer consisting only of gallium arsenide was used.

This effect is achieved through the appearance of the so-called "quantum well" effect and the superlattice effect. The "quantum well" effect occurs in that active area when a very thin layer of a second semiconductor material between two layers of a

PIIN 10.639 2 1-3-1984

first semiconductor material with a larger band gap than that of the second material is included. This leads to the effective band gap in the thin layer of the second material is larger and therefore the wavelength of the generated radiation is smaller. The superlattice effect occurs as a result of the superlattice structure and leads to a conversion of the "indirect" semiconductor material in relation to the band transitions of the charge carriers effective, "direct" semiconductor material. This increases the radiation transfer probability of the charge carriers, so that a high radiation density can be achieved. Reference is made to a description of the “quantum well” effect i.a. on "Quantum Well Heterostructure Lasers" by N. Holonyak and others, I.E.E.E. Journal of Quantum Electronics, Issue GE-16, No. 2, Feb. 1980, pages 170-186. In the production of such superlattice structures, the thickness of the active layers between 2 nm and 50 nm and the thickness of the barrier layers between 1 and 20 nm, high demands are made on the periodicity of the structure.

The invention now has the object, inter alia a

To create semiconductor arrangements for LEDs or lasers in the in particular at room temperature, the highest possible radiation density occurs at a certain current intensity.

Another object of the invention is to create a laser of the above structure that emits radiation emits with as short a wavelength as possible.

According to the invention, a semiconductor device of the type mentioned at the outset has the characteristic that the second material is attached in the form of a wire or layer is, the dimensions of the wire or the layer, in a direction perpendicular to the wire or the layer corresponds to at most the thickness of two monomolecular layers of the second semiconductor material and the dimension in a longitudinal direction of the wire or the layer at least one hundred times the thickness of the wire or corresponds to the layer.

The invention is based, inter alia, on the knowledge

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PHN 10,639 X 1-3-1984

that the wires or layers mentioned are thin enough, that these can be regarded as normal impurities for the surrounding semiconductor material while they nevertheless with modern techniques such as molecular bundle epitaxy (MBE) or metallo-organic vapor phase epitaxy can be applied in a structured manner.

In addition, the invention is based, inter alia, on the knowledge that in the event that the wires or layers consist of semiconductor material with a smaller band gap than the matrix material, but still a "quantum well "-like disturbance effect occurs such materials are selected that a good lattice adaptation occurs. The dimensions in the longitudinal direction the layer or the wire are sufficient to

γ _ζ to ensure the presence of bound states.

In addition, the invention is based on the knowledge that in the mentioned GaP: N structure of the above Attachment well-structured layers (wires) of nitrogen atoms in the matrix material without complex formation of the nitrogen in the actual matrix material. this will achieved in that the layers (wires) are attached at relatively low temperatures and also later no heat treatment takes place. There is therefore no absorption of the electromagnetic generated in the matrix material Radiation on.

A semiconductor device according to the invention

furthermore has the advantage that only the structured layers or wires are subject to strict requirements in in relation to the dimensions (no more than 2 monomolecular layers thick), but not the structure absolutely needs to be periodic.

According to a first preferred embodiment order the first and second materials from aluminum arsenide and gallium arsenide, respectively. A laser with one of these active semiconductor area emits red (approx. 63Ο nrn) light off (in air).

According to a second preferred embodiment,

PHN 10.639 / Γ 1-3-19Β4

make the first and second material from aluminum phospläd and gallium phosphide, respectively. A laser with such an active semiconductor region emits green (about 54θ nm) light off (in air).

In both cases, there is also a good lattice match between the two materials. In the mentioned Examples run the requirement with respect to the thickness or the diameter of the layer or the wire in addition to the fact that this is at most 0.6 nm. Other examples of a second material in one Matrix material with a larger band gap are, for example: indium phosphide in gallium phosphide and iadum arsenide or gallium antimony in gallium arsenide. In addition to lasers, these materials can also be used to manufacture LEDs that have a high luminous efficacy at low amperage.

In addition, the deformation of the lattice here leads to an increased binding energy of the excitons (hole-electron pairs) due to a less good lattice adaptation, so that the Transfer probability of electromagnetic radiation is increased.

The latter (increase in the transition probability due to an increased binding energy of the excitons) also occurs when the second material is gallium nitride and the first is gallium phosphide, although in this case it is second material has a larger band gap.

Embodiments of the invention are shown in the drawing and are described in more detail below. Show it:

Fig. 1 is a schematic view of a light emitting Diode (LED) according to the invention,

2 shows a schematic enlarged section by part of the arrangement according to FIG. 1,

FIG. 3 shows a modification of FIG. 2 according to FIG Line III-III in FIG. 4, which shows the top view of an active layer in an LED according to the invention is,

Fig. 5 is a schematic representation of the energy levels in the active material,

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PHN 10.039 tf | _ ·) - | 08 / | ·

6 shows a laser according to the invention, and FIG. 7 shows a modification of the arrangement according to the invention. The figures are schematic and not true to size, with the dimensions in the thickness direction in particular being greatly exaggerated for the sake of clarity in the sections. Semiconductor regions of the same conductivity type are generally hatched in the same direction; In the figures, corresponding parts are usually given the same reference symbols.
The light emitting diode (LED) 1 according to Fig. 1 contains an η substrate 2 made of gallium arsenide, the example

1 8 wise with sulfur with a concentration of about 10 Atoms / cm is doped. -A-uf this substrate is for example through molecular bundle epitaxy (MBE) or metallo-

ib organic vapor phase epitaxy (ΠΟΥΡΕ) the n-type active layer 3 attached. Furthermore, the arrangement of FIG. 1 is provided with an annular ρ zone 4 which is obtained in the desired shape, for example with the aid of a second epitaxy step after etching. the Zone 4 is provided with a metal layer 5 for the purpose of contacting. The other diode contact is via a metal layer 6 contacting the substrate.

The active layer 3 consists of a matrix material 7 »in this example n-type aluminum arsenide, the impurities causing η conductivity being added to the matrix material during epitaxial growth have been.

According to the invention (see FIG. 2) the material 7 is provided with a second material in a structured manner. In this example, the layers 8 made of gallium arsenide have grown to a thickness of only one mono-molecular layer of gallium arsenide (about 0.3 nm). The layer is also at least 100 times (about 30 ^nm ) longer or wider. In the example in question, the matrix material 7 contains several layers 8, which are separated by layers of aluminum arsenide of about 10 ionomolecular layer thicknesses of aluminum arsenide at a distance

PHN 10. 63S) Z 1-3-I 9 "'+

about 3 µm apart. This distance is enough from the potential disturbances (bound states) of two different layers. 8 not to be influenced by one another.

The layers 8 do not need to cover the entire surface of the area 3, but may as Partial layers are attached at different heights, as shown in Fig. 3, where the layers 8, 8,8,8 lie in different planes and partially overlap one another (see Fig. 4).

Fig. 5 shows a schematic energy diagram of the layer 3 according to the line V-V in If the layer 8 is present, a disruption occurs in the band structure of the matrix material 7, which has a different shape has than in the case of a "quatum wells" as indicated by the dash-dotted line 9. In this latter Case there are a number of discrete energy levels for holes and electrons within the quantum well, radiation recombination being essentially between the lowest level in the conduction band and the highest Level of the valence band of the material that causes the "quantum well" occurs (see, for example, "quantum well Heterostructure Lasers "by N. Holonyak Jr. and others, published in I.E.E.E. Journal of Quantum Electronics, Booklet Ge-16, No. 2, February I98O, rare I70 etc. especially pages 170-171) · The recombination takes place with a frequency between those that belong to the band gaps of the assembled materials. In the embodiment according to the invention (a Interference with a layer thickness of at most two monomolecular layers) the layer 8 is practically considered to be Pollution. Seen in the direction of the line V-V, the disturbance introduced thereby (quantum mechanical as A symmetrical shallow potential well can be considered, which can be shown that there is only an energy level in is available near the top of the trough (see, for example, Landau and Lifshitz "Quantum Mechanics", 2nd Edition, Pergarnon Press, 1965, pages 65-67, IO9-IIO,

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40

PHN 10,639 p

156). Holes or electrons bound by a layer S. therefore apply energy levels immediately above or below the valence band or the conduction band of the matrix material and form bound with electrons or holes Excitons. The assigned energy distance, which is a measure of the frequency of the emitted electromagnetic Radiation is indicated in FIG. 5 by the reference numeral 10.

The layer 8 behaves like a so-called "iso-electronic surface", i.e. like a layer of impurities, which present themselves as iso-electronic radiation centers. Such centers are caused by impurities which have the characteristic property of an electron and a hole (a so-called Exciton) to bind with a finite energy without itself to be able to form a pure charge or exclusively an electron or a hole.

Because of the high binding energy, in this case resulting from the energy level of the symmetrical potential well, there is now recombination in the gallium arsenide layer at a frequency associated with an energy almost the same as the energy gap in the aluminum arsenide corresponds, possible. This way, radiation is using a shorter wavelength than in the real one Material of the layer 8 is possible.

Due to the high binding energy mentioned, the excitons also have great stability, which together with the high density in only one iso-electronic layer the possibility of radiation recombination with the frequency associated with the binding energy mentioned is significantly increased, especially at room temperature. The excitons remain, as it were, bound to the layer. this results in a high radiation density along the layer, which is not disturbed by losses elsewhere in the material, because the radiation is mainly generated along the layer, while the aluminum arsenide also produces practically none Contains recombination centers. In the example in question, there are also no radiation losses at lattice defects

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on μ η rl: '. vy.:r cladurcii., class aluminum arsenic and gallium arsenide practically have the same lattice constant. The same example applies to sent or wires out Gallium phosphide in alurainiuraphosphide. LEDs with one have such an active layer structure, therefore the advantages a shorter wavelength, a higher degree of efficiency, while also the service life is longer.

In layers of gallium phosphide in indium phosphide or from gallium arsenide in indium arsenide or in gallium antimony there are differences in the lattice constants on. This could introduce recombination centers; however, it is known to be in very thin layers (about 10 monomolecular layers) the lattice deformation is elastically compensated without creating recombination centers (see: Continuous 3 ^ 0 K-Laser operation of strained Superlattices, by M.J. Ludowise and others, Appl. Phys. Lett. 42 (6), I5. March 1983, p. 487). Well At the same time, the binding energy of the excitons becomes essential increased so that they have greater stability.

A similar advantage applies when attaching layers or wires made of gallium nitride in gallium phosphide, although the matrix material has a smaller band gap As the second material, however, due to the structured attachment, it has a higher pure exciton density in gallium phosphide can be obtained, namely on iso-electronic Surfaces or wires than according to the known method. Because also in the matrix material itself now there are no undesired regeneration centers, an LED with a higher yield is thus obtained.

The arrangement according to FIG. 6 shows a semiconductor laser 11, constructed from a substrate 12 made of highly doped η-conductive gallium arsenide (GaAs), on which several layers have grown with the help of molecular bundle epitaxy or metallo-organic vapor phase epitaxy. The substrate 12 has a thickness of 200 μm, for example

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and is doped with about 5 · 10 7 selenium atoms / cm. Thereon are a layer I3 made of highly doped 11-conductive gallium

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PHN 10.639

arsenide (GaAs) with a Dici.e of about 0.3 / urii and with a doping of 3 · 10 'selenium atoms / cin ^, one layer

14 of highly doped η-type Ga_ "Al _o As (1.5" 10 selenium atoms / cm) having a thickness of about 0.5 / ^um and a η-type layer 15 of aluminum arsenide having a thickness

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of 1.5 / μm and a doping of 8 "10 selenium atoms / cm grown.

The active layer 16 is applied thereon with a thickness of approximately 50 μm. This layer consists of one Matrix material made of aluminum arsenide, in which structured Way one or more layers of gallium arsenide are attached according to the structure of the active layer 3 of the LED. as has been described with reference to FIGS. 1 to 4.

The laser 11 also contains a zinc-doped 1.5 μm thick p-conductive layer 17 made of aluminum

'17/3

arsenide with a doping of about 3 · 10 6 atoms / cm and with a highly doped p-conductive contact layer 18 with

19/3 a doping of about 1.10 atoms / cm and with a Thickness of 0.1 / µm.

Furthermore, the laser 11 has metal contacts 19 and 20 provided for current injection. When crossing a certain threshold current, the laser 11 becomes electromagnetic Emit radiation in a direction perpendicular to the plane of the drawing.

In the arrangement according to FIG. 6, the width of the active region is limited to, for example, 6 μm and by the fact that a proton bombardment is carried out with the electrode 20 as a mask, which extends up to the Area which is delimited by the dashed line 21 extends. This makes area 16 a large part made inactive and the laser effect only occurs in a narrow strip.

The same can be achieved by using the electrode 20 as a mask to form part of the layer structure is etched away. In this case an arrangement is obtained as shown in a schematic manner in FIG where the reference numerals have the same meaning as in Fig. 6. The etched cavity is mostly later

PHN 1Ο. (> 39 Vf 1-3-19 ^

again filled with a suitable protective material.

It should be clear that the invention is not limited to the examples presented above rather, several modifications are possible for the person skilled in the art within the scope of the invention. So you can for select the active layer several other combinations of materials, which then, for example, radiation with a emit larger wavelengths. For the matrix material For example, indium phosphide can be selected and indium antimonide or indium arsenide for the layers. Even appropriately chosen ternary or quaternary compounds can be used. In addition, as already mentioned, instead of layer structures, wire-like structures are attached.

In addition, electron injection can be used instead of current injection be applied, for example when a layer of one of the above compositions in a Arrangement is used as described in the applicant's Dutch patent application no. 83OO63I will.

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Claims (10)

PHN 10,639 J- £ 1-3-1984 PATENT CLAIMS: Semiconductor arrangement for generating electromagnetic radiation in an active region of a first semiconductor material? the structured overlay is provided with a second semiconductor material, characterized in that the second semiconductor material is attached in the form of a wire or a shaft, the thickness of the wire or the layer in a direction perpendicular to the wire or the layer at most the thickness corresponds to two monomolecular layers of the second semiconductor material and the dimension in a longitudinal direction of the wire with respect to the layer corresponds to at least one hundred times the thickness of the wire or the layer.
2. Semiconductor arrangement according to claim 1, characterized in that the first semiconductor material has a larger band gap than the second material. 3. Semiconductor arrangement according to Claim 2, characterized in that the structure of the second semiconductor material contains a plurality of wires or layers with a mutual spacing greater than the thickness of eight monomolecular layers of the first semiconductor material. 4. Semiconductor arrangement according to claim 2, characterized in that the first semiconductor material made of aluminum arsenide and the second semiconductor material consists of gallium arsenide. 5. Semiconductor arrangement according to claim 2, characterized in that the first semiconductor material is made of Aluminiurirphosphid and the second semiconductor material consists of gallium phosphide. 6. Semiconductor arrangement according to claim 4 or 5 »characterized in that the thickness of the layer or the diameter of the wire is no more than 0.6 nm. 7. Semiconductor arrangement according to claim 1, characterized in that OHlIlOl PHN 10.639>? 1-3-1984 indicates that the first semiconductor material consists of gallium phosphide and the second semiconductor material consists of gallium nitride.
8. Light-emitting diode according to one of the preceding Claims, characterized in that there is an emitting pn junction between the active semiconductor area, which has a first conductivity type, and a second semiconductor zone with one opposite to the first Line type is located. 9 · Light-emitting diode according to claim 8, characterized in that the active layer is on a layer ■ · of the second type of conduction is attached and the pn junction furthermore you have a ring through the active layer second conductivity type buried region therethrough is formed. 10. Semiconductor laser according to one of claims 1 to 7> characterized in that the active semiconductor region is schichtförinig and is between on the one hand several Semiconductor layers of the first conductivity type and, on the other hand, a plurality of semiconductor layers of a second, the first opposite line type is located.