WO2001078155A2

WO2001078155A2 - Wavelength-selective pn transition photodiode

Info

Publication number: WO2001078155A2
Application number: PCT/EP2001/004287
Authority: WO
Inventors: Michael Humeniuk; Hartwin Obernik; Bernd Kloth
Original assignee: Epigap Optoelektronik Gmbh
Priority date: 2000-04-12
Filing date: 2001-04-12
Publication date: 2001-10-18
Also published as: AU6386101A; DE10019089C1; WO2001078155A3

Abstract

The invention relates to a particularly narrow-band photodiode, whereby a photoelectrically active layer (3, 20) and the layers thereof abut against different layers on the two surface sides thereof. A photoelectric stop filter layer (4, 22) for shorter-wave radiation of monolithically integrated semiconductor material is formed on the radiation-exposed side of the photoelectrically active layer (3, 20). The energy band gap (EGA(x)) of said stop filter layer is provided with a greater value than the energy band gap (EGB(x)) in the directly adjacent layers of the photoelectrically active layer (3, 20) and the remaining side is sealed by means of a hetero transition between a substrate (1) or a buffer layer (2) being situated above said substrate (1) and the photoelectrically active layer (3, 20) with band discontinuity within the appurtenant energy band of the moveable minority carriers, whereby said discontinuity forms an access barrier (ΔB) for minority carriers of the substrate (1). As a result thereof, minority charge carriers of the substrate (1) or the buffer layer (2) cannot reach the photoelectrically active layer (3, 20).

Description

Wavelength selective pn junction photodiode

description

The invention relates to a wavelength-selective pn-transition photodiode made of ternary or quaternary III-V mixed connections for a freely selectable, visible or infrared spectral range with a stack arrangement of several functional zones normal to the direction of incidence of the electromagnetic spectrum. The photodiode is biased by an external electrical voltage, in particular in the blocking direction.

[002] Photodiodes are used to convert optical to electrical signals in the field of optical telecommunication technology, in customer-oriented optoelectronic circuits and interconnectors, and in scientific and industrial devices for photometry, spectrophotometry, chromatography, calorimetry, medicine and biotechnology.

The new areas of application develop contrary to the original tendency in fiber optic communication technology with regard to new areas of application in the visible and ultraviolet spectral range. Accordingly, new requirements for the performance and technology of this traditional product group arise from the new fields of application of photosensitive semiconductor diodes.

In addition to the optical efficiency, the spectral expansion of the photosensitivity, the temporal response and the temperature sensitivity of the photodiodes as well as the stability under high optical excitation densities are the most important application parameters. [004] Photosensitive electrical components with a pn junction, in which a photocurrent is produced by the generation of electron-hole pairs by the internal photo effect in the volume or in the space charge zone and their subsequent separation by electrical fields, have been known since 1941. For example, US Pat. No. 2,402,662 describes the photosensitivity of silicon of high purity and with a pn transition zone in volume by means of a spectral sensitivity between 0.5 and 1.3 μm and a peak at 1.1 μm.

The long-wave limit λ _{0G of photosensitivity} is determined by the bandgap E _{G of} the semiconductor (λ _0G = 1.24 / E _G ) - the short-wave limit, on the other hand, is determined by the part of the _high- energy photons injected into the semiconductor that are not reflected on the surface, which already contribute to the photocurrent after their absorption.

The traditional element semiconductor silicon covers a very wide photosensitive spectral range and the absorption of light grows gradually with increasing energy and not nearly as steep as with direct semiconductors, for example GaAs, (see G.Stillman and CM. Wolfe, Semiconductors and Semimetals, 12 (1977), pp. 291-393). The high IR sensitivity of the Si photodiodes can be desirable or undesirable. The aging of the Si photodiodes when exposed to high UV levels is just as disadvantageous as the limited working temperature range and the strong non-uniformity of sensitivity at different wavelengths (TC Larason et al. "Spatial uniformity of responsivity for Si, GaN, Ge, InGaAs Photodiodes" in Metrologia, 35 (1998), pp. 491-496). The expansion and also the limitation of the sensitivity range of the photodiodes are two disjunctive objectives that are mastered in a fundamentally similar way.

One structure is based on supplementing the semiconductor with additional optical parts from the outside. The other structure uses the modification of the semiconductor structure in the form, shape, composition and contact of the optically active zones involved. Other structures are based primarily on special operating conditions such as the polarity and the size of the electrical bias.

Is a fixed course of the spectral sensitivity of the photodiodes for use e.g. The aim in exposure meters of the cameras is to adapt the diode sensitivity to the sensitivity of the human eye or the film. Optical attachments in front of the diode are then used for this. According to DD-A 143 839, for example, selected optical filter glasses are used.

[007] In UV water disinfection systems using Hg low-pressure or medium-pressure lamps, sensors based on SiC photodiodes are used as monitoring units for measuring the irradiance. The selectivity required is adapted to the requirements by Schott edge filter WG 305. (H. Hensel et al. In the journal gwf Wasser Abwasser, Volume 138 (1997), No. 10, pp.531-536). Instead of filter glasses, according to DE-C 26 46 424, filter molded materials are also inserted into epoxy injection molding or casting resins, which form a layer-like covering or covering of the radiation-sensitive semiconductor. With the choice, concentration and combination of the pigment dyes, an individually determined color correction of the sensitivity of the photoreceptor is carried out. The aim of this correction is to keep the extraneous light incident from wavelength ranges below 700 nm away from the semiconductor and to suppress the interference currents that otherwise result in the working range of the receiver near the emission band of GaAs light emitters. Suitable mixtures for other useful wavelengths have to be composed again and again.

For the detection and measurement of the intensity, preferably monochromatic radiation, according to DD-A 158 198 pn or pin photodiodes are additionally provided with an antireflection layer and a tailored sequence of interference layers to avoid reflection losses for a predetermined wavelength range. Switching to another wavelength range is not possible with the same layer sequence.

UV-light-permeable filter layers on a first photodiode and UV-light-impermeable filter layers on a laterally arranged in the same semiconductor body second photodiode are used according to CH-A 684971 to build a UV-sensitive sensor that is used for flame monitoring in control equipment of incinerators or UV light measuring devices can be used. A low-effort determination of the spectral power distribution of radiation sources such as laser or luminescent diodes is possible according to DD-A 230 633 by decomposing the spectrum with a dispersion element and scanning the spectrum with a row of photosensitive CCD elements.

Modification of the structure of the structure has been attempted in various ways. In order to achieve a narrow spectral sensitivity and to improve the signal-to-noise ratio in pn-transition photodiodes, the thickness of the GaAs absorbing semiconductor was varied in US Pat. No. 3,506,830. Due to the large mobility and diffusion length of the minority charge carriers and the low doping (3xl0 ¹⁶ at / cm ³ ) in the zones on both sides of the pn junction and the polarity of the pn junction in the reverse direction with approx. 2 volts, the peak wavelength λ _p shifts from 896 nm at 200 μm to 901 nm at 400 μm and 905 nm at 800 μm with the same half width Δλ of 200 nm only by a few nm.

In the event that the light absorption occurring in a limited local area of a photodiode is too small, it can be provided according to DE-C 32 05461 on the light entry side and on the opposite side with reflectors, so that in a predetermined wavelength range a resonator structure is created.

[014] An increased efficiency in the area of eye sensitivity was achieved according to SU-B 1.123.069 by first epitaxing a slightly graduated Al-GaAs layer on a GaAs and then a substantially broadband AlGaAs window layer. This window layer on the light entry side ensures due their bandgap of up to 2.9 eV, a uniform expansion of the spectral sensitivity in the direction of the short-wave edge. According to this patent specification, the steepness of the long-wave edge of the sensitivity can be influenced by the gradient of the bandgap (in eV / cm) in the region covered by the space charge zone.

[015] In order to be able to separate the signal groups of different wavelengths transmitted via the same glass fiber without the effort using a sensitive fiber-filter-photodiode combination, the stack arrangement of a nip-InP-InGaAsP was described in GB-C 2.030.359. Proposed photodiode and a downstream pin-InGaAsP-InP photodiode. The absorption layer in the first photodiode has a band gap of 1.14 eV and the second one of 0.89 eV. While the p-contact is used by both diodes, the n-contacts are diode-specific. The selective sensitivity of the first diode with a half width of 190 nm is 1020 nm. The second diode has a half width of 230nm and its highest sensitivity at 1215nm. As a result, the signals at 1.1μm and 1.3μm should be transmitted simultaneously, but then be separated.

An expansion of the spectral analysis range from UV to IR without a separate spectral decomposition was achieved in DD-A 292 771 by a semiconducting multilayer sensor. Radiation-sensitive layers, the thickness of which increases in the direction of incidence, are separated from one another by potential barriers and are exposed to different potentials. EP-A 0 901 170 has proposed a wavelength-selective photodiode module for fiber transmission of signals for media such as telephony, fax or television picture, which responds to wavelengths around 1.3 μm and from 1.5 to 1.6 μm. It should allow bilateral operation and simultaneous transmission on one fiber. The bilateral operation via the fiber is based on a wavelength-selective beam splitter and beam splitter function (Wavelength division and combination multiplexer - WDM), by which 1,3 and 1,55μm signals were separated with the help of special mirrors. Since these mirrors make the photomodules complex and unwieldy, the photodiode modules should be simplified.

According to EP-A 0 901 170, page 4, column 5, paragraph 0023 use is made of the fact that a semiconductor of sufficient thickness can absorb all light whose photon energy is greater than its band gap. So from the publication of T.P. Pearsell and M. Papuchon, "The GaO .47In0.53As Homojunction- Photodiode - a new avalanche photodetector in the near infrared between 1.0 and 1.6 μm" in Appl. Physics Letters, Vol. 33 (1978), H. 7, pp. 640-642, it is known that optical signals which are fed in not via the epitaxially coated surface, but rather via the InP substrate window, have a short-wave cut course of the spectral sensitivity.

[019] EP-A 0 910 170 uses the transmittance insert inherent in the InP substrate and / or in an InGaAsP layer grown on the substrate side for the separation of adjacent wavelength ranges. As a result, the photomodule manages with fewer parts, less space and lower costs, but is technically limited due to the intrinsic properties of the rear coupling of the signal. The length of the path and the risk of multiple reflection of the photons of the optical signal in the thick substrate and the diffusion or drift of the charge carriers generated optically in the substrate or in the InGaAsP layer close to the substrate into the actual photosensitive layer of the photodiode weaken the selectivity of the spectral sensitivity above all the speed of the time response. Due to the delayed migration of charge carriers that have arisen outside the pn junction and the space charge zone emanating from it, the edges of the current pulses of the diode do not follow the edges of the pulses of the optical signal in real time. The bandwidth of the transmission path is smaller than with the otherwise usual Burus structures with the etched-out substrate window.

[020] Further options for influencing the sensitivity are based on the suitable application of defined electrical potentials or potential differences to the active zones of the photodiode.

The use of the operating conditions of the photodiodes to simplify the peripheral electronics and the easier installation in integrated circuits was attempted using optoelectronic switches in accordance with GB-C 2.078.440. The photodiode, which is contacted on two surfaces and can be exposed over both surfaces, contains a 2μm thick p-type InP layer on an n-type InP substrate, followed by a 2μm-thick, narrow-band InGaAs layer. With small reverse voltages between 0 and 15 V, the space charge zone is not extended into the heterojunction p-InP-p-InGaAs. The photons absorbed in the InGaAs and the resulting electron-hole pairs are not perceived in the electrical circuit and the photodiode is switched off. With higher external chip Between 20 and 80V, the space charge zone fills the entire absorbent InGaAs layer and the generated charge carrier pairs are separated and led directly or through the heterojunction to the next contact.

According to DE-A 32 21 335, a photodiode in GaAs-AlGaAs technology is used for spectral analysis of the composition of the light in measuring devices of physical or chemical sizes. An n-doped AlGaAs layer, a thin weakly p-conducting AlGaAs layer and a p-doped GaAs layer are located on an n-doped substrate. On the light entry side, the n-GaAs layer up to the n-AlGaAs layer is removed. At low bias voltages, only the higher-energy part of the spectrum absorbed in the AlGaAs is recorded and only at higher voltages also the lower-energy part absorbed in the p-GaAs. The measure for the position of the spectrum is obtained from the quotient of the intensities at the two different bias voltages determined with an electronic circuit.

When operating the spectrometer diode according to DE-A 37 36 203, the wavelength sensitivity of the diodes lying in the region with a constantly changing band gap is changed periodically by modulating the reverse voltage.

The invention has for its object to provide a photodiode made of ternary or quaternary III-V mixed compounds, which is very narrow-band sensitive in a freely selectable, visible or infrared spectral range, has a high uniformity over the active area and that has the necessary means monolithically integrated in the semiconductor body, is compatible with mass production-compatible technologies for diode production and does not have to resort to special external optical attachments or particularly optimized operating circuits or voltage modulation. According to the invention the object is achieved by the features of claim 1. Appropriate configurations are the subject of the subclaims.

[026] Then, in order to determine the sensitivity limits with regard to the detectable photon energy, a photoelectrically active layer and its layer layers on its two surface sides abut against layers of different chemical composition. On the irradiated side of the photoelectrically active layer, a photoelectric blocking filter layer for short-wave radiation is formed from monolithically integrated semiconductor material, the energy band gap (E _GA (x)) of which is set via at least two components of the III-V mixed connection and a greater value than the energy band gap ( E _G B (X)) in the directly adjacent layer layers of the adjacent semiconductor material of the photoelectrically active layer on ice. The minority charge carriers generated optically here are prevented by the design of the spatial profile of the energy band structure and the expansion of the barrier filter layer in connection with a suitable doping profile from reaching the adjacent photoelectrically active layer. After a pn junction, the blocking filter layer is followed by the photoelectrically active layer, the semiconductor material of which is distinguished by a large diffusion length of the optically generated minority charge carriers and is detected in operation by a space charge zone. The photoelectrically active layer is formed by a heterojunction between a substrate or a buffer layer lying above the substrate and the photoelectrically active layer with a band discontinuity forming a barrier to access (ΔB) for minority carriers from the substrate in the course of the associated energy band of movable mino- rity carriers completed, as a result of which no minority charge carriers from the substrate or the buffer layer can get into the photoelectrically active layer.

The photodiode according to the invention is based on an operating principle for deliberately controlling the minority charge carriers in the different functional zones of the semiconductor body and a resultant determination of the sensitivity limits with regard to the detectable photon energy and the effectiveness of its conversion. The semiconductor body of the photodiode contains a stack of at least three functional zones, which lie one above the other in layers and, in the direction of light incidence, consist of a barrier filter layer, a photoelectrically active layer and a solid photoelectrically passive base body consisting of the conventionally load-bearing semiconductor base or a semiconductor base and an overlying lattice adjustment buffer , In the diode body controlled with respect to the minority charge carriers, the service life of the minority charge carriers jumps along the light incidence path during the transition from the first functional zone - the barrier filter layer - to the second functional zone, the photoelectrically active layer, by about an order of magnitude if necessary. also much more.

Successful for a steep short-wave limit of the spectral photosensitivity of the photodiode is that the diffusion length of the minority charge carriers in the barrier filter layer is kept significantly less than that

Thickness of this layer. For the control of the diffusion length in the barrier filter layer, the x value in the A _x B _ι _ _x C connection or the AC _X _ _X D _x connection can be used. In the Al _x Ga _. _ _{x As} connection this is the aluminum portion, in the In _ι _ _x Ga _{x As} connection it is the gallium portion and in the GaAs _ι _ _x .P _x connection the phosphorus portion.

The type of dopant and the amount of its doping in this layer can also be used as a further control means independent of the x value. A type of foreign atom influencing the conductivity is preferably selected and the type of conductivity is adapted to that of the barrier filter layer. However, isoelectronic impurities or other electronically neutral foreign atoms can also be used

The effect of the barrier filter layer can also be enhanced by a cover layer with a high surface recombination rate.

[032] To limit the short-wave sensitivity, an optoelectronic blocking filter is used, which is attached as a monolithically integrated, layer-shaped, semiconducting optical absorption window for a selected wavelength range on the light entry side of the photodiode. Under all electrical operating conditions of the photodiode, this blocking filter has an almost uniform electrical potential or only slightly varied in the direction of the light entry over the thickness of its filter layer. Separating electrical drift fields are deliberately kept away from the charge carrier pairs that are created by the internal photo effect. [033] The charge carrier pairs which have arisen in this layer and remain almost stationary in this layer disappear here through immediate radiationless recombination. The type of conductance of the semiconducting barrier filter layer is subordinated to the implementation options for equipotential conditions in the layer and for a small diffusion length in the layer.

A change of control type takes place in the semiconductor body of the photodiode between the barrier filter layer and the photoelectrically active absorption zone.

To avoid the influence of the high surface recombination speed in areas next to the pn junction on the saturation blocking current, the top layer of high surface recombination is interrupted in a ring around the pn junction according to a variant of the invention. Both pit-like etching and diffused protective rings against cross currents on the surface contribute to this.

To increase the efficiency in the sensitivity range of the photodiode, the light entry surface above the blocking filter is expediently covered with an antireflection layer, which should be matched specifically to the center wavelength of the photosensitivity.

Since the minority carrier lifetime in p-doped LPE GaAs / AlGaAs structures on (100) -oriented n-type GaAs substrates according to studies by JP Bergman et al. , published in the journal Journal Applied Physics 78 (1995) Issue 10, pages 4808-4810 strongly depends on the temperature, special attention must be paid to the temperature stability of the short-wave flank of the wavelength-selective sensor. If, as shown by Bergman, the Le- If the lifetime of the minority charge carriers increases monotonically by a factor of 3 - 10 in the working temperature range, the selectivity of the sensitivity of the photodiode could deteriorate and the half width Δλ and the position of the center wavelength λ could be shifted.

The invention is then to be described in more detail with reference to two exemplary embodiments. Show

1 shows the basic structure of the functional elements of a wavelength-selective sensor from a narrow-band pin AlGaAs photodiode,

2 shows the variation of the band gap along the light path in the semiconductor body,

3 shows the energy band diagram and the range of the photons of different energy in the photodiode,

4 shows the doping profile in the semiconductor body of the photodiode,

5 shows the absolute spectral photosensitivity of a p ⁺ pn ^" n-Al _x Gaι_ _x As photodiode at room temperature,

6 shows the dependence of the photoelectric properties on the temperature, a.) Photocurrent with a fixed bias, b.) Wavelength selectivity,

Fig. 7 a) the variation of the band gap along the

Light path in the semiconductor body, b) the doping profile in the semiconductor body of the photodiode and

8 shows the mesa structure of a wavelength-selective sensor made of a GalnAsP photodiode. 1st embodiment

Figure 1 shows a basic structure of a photodiode according to the invention. A multilayer structure is deposited on a uniformly conductive single-crystalline n-conductive substrate 1 made of a binary compound semiconductor with selected orientation using liquid phase epitaxy. First of all, a thin structure-adapting buffer layer 2 is expediently formed from semiconductor material of the same conductivity type, in which the doping still has an increased concentration level. However, this buffer layer 2 is not absolutely necessary for the function of the photodiode according to the invention. In the subsequent layer growth, the side of the disk to be coated is wetted with a liquid phase, to which an element of the third or fifth group of the periodic table is added, which increases the band gap in the layer by several tenths of an eV compared to the band gap E _{GS of} the substrate 1 and thus causes a jump 10 in the band gap (FIG. 2). It is important to ensure that the photoelectrically active layer 3 to be formed soon changes into a layer with a decreasing gradient of the band gap after the significant jump 10 in the band gap E _GB (x) at x = d _E (FIG. 2). The gradient range of the band gap E _GB (x) ranges from x = d _A to x = d _E and has, for example, an average value of 5 x 10 ^"3 eV / μm. The photoelectrically active layer 3 has a thickness d _E - d _A of for example 5μm and is only very weakly doped.

A further compound semiconductor layer is now deposited, which is intended to perform a filter function in a double sense. This barrier filter layer 4 initially grows again with a bandgap jump 9 of, for example, 0.15 eV compared to the photoelectrically active layer 3. With increasing layer thickness, the band gap also decreases here with an average gradient of 7.5 x 10 ^{~ 3} eV / μm. The barrier filter layer 4 is provided with a high acceptor concentration over the entire thickness. The p-type barrier filter layer 4 is 5 - 10 μm thick and forms the window for the light to enter the photodiode. The large part of the high-energy photons is absorbed in the barrier filter layer 4 and converted into electron-hole pairs. Part of the barrier filter layer 4 is designed as a highly doped cover layer 5.

[041] An optically adapted thin layer is made over the blocking filter layer 4, which layer consists of A1 ₂ 0 ₃ and takes over the function of an anti-reflective layer 6 against reflection losses in the desired wavelength range. The incident radiation penetrates into the photodiode via the anti-reflective coating 6 on the front with its entire bandwidth (band gap E _GE ). The signals pass through a front contact 7. The front contact 7 and a back contact 8 serve to bias the photodiode in the reverse direction and to decrease the photocurrent when illuminated.

FIG. 2 shows the spatial dependence of the band gap along the light path x through the anti-reflective layer 6 from A1 ₂ 0 ₃ , through the barrier filter layer 4 with the gap E _GA (x) and through the photoelectrically active layer 3 with the gap E _GB (x ) into the buffer layer 2 and the substrate 1 with the energy gap E _GS (x).

[043] FIG. 4 shows the profile of the doping concentration through the layer structure of the example according to the invention. The profile part 11 represents the doping in the p-type region. The profile part 12 relates to the doping in the n-type region. [044] FIG. 3 shows the photoelectronic and electronic mode of operation on an AlGaAs photodiode.

The very long-wave optical signal λ (C) here represents radiation above 780 nm. It penetrates into the substrate 1 and generates electron-hole pairs there. So that the minority charge carriers of these pairs cannot get into the photoelectrically active layer 3, the minority carrier lifetime is reduced in the buffer layer 2 by a high doping. For example, the doping concentration in this area can be set to values greater than 10 ¹⁸ cm ^"3. In addition, the jump 10 in the energy band gap between the buffer layer 2 and the photoelectrically active layer 3 prevents the penetration of minority charge carriers from the substrate 1 into the space charge zone of the photoelectric active layer 3 so that the radiation λ (C) does not contribute to the photocurrent The radiation λ (B), which represents a wavelength range from 710 to 780 nm, penetrates into the photoelectrically active layer 3, is absorbed there and generates electrons - Hole pairs that are separated in the space charge zone and thus contribute to the photocurrent.

The radiation λ (A), which contains wavelengths less than 710 nm, is completely absorbed in the barrier filter layer 4. However, the generated free minority charge carriers are made to disappear within the barrier filter layer 4 by recombination. This is achieved in particular by a sufficiently high doping concentration, which results in a reduction in the minority carrier lifetime, in particular in the area of the barrier filter layer 4 near the surface. In addition, the minority carriers are prevented from moving in the direction of the space charge zone by the gradient of the band gap. This design of the barrier filter layer 4 achieved that the photons absorbed here can not contribute to the photocurrent of the photodiode.

The spectral photosensitivity of a pn junction photodiode made of AlGaAs is given in FIG. 5. Compared to a UN-sensitive GaP photodiode or a broadband conventional Si photodiode, the diode designed according to the invention according to curve 13 is very narrow-band sensitive around the center wavelength λ _M = 740 nm. The edge steepness becomes essential due to the change in the band gap within the barrier filter layer 4 for the short-wave flank and determined by the change in the band gap in the photoelectrically active layer 3 for the long-wave flank. The spectral position of the flanks can be set relatively independently of one another by adjusting the band gaps in the barrier filter layer 4 and in the photoelectrically active layer 3. The spectral half-width Δλ is therefore not determined electronically by the semiconductor but can be freely selected.

The effectiveness of the conversion of the optical signal into an electrical signal in the selected wavelength range can be seen from the clear approximation to the ideal yield. Despite the filtering, the external quantum yield remains up to 78% higher than that of the broadband sensitive photodiodes of the element semiconductors.

[047] The special feature of the photodiode according to the invention is, inter alia, the extended operating temperature range. Figure 6a shows that the photocurrent I _{PH of} the 74Onm photodiode under constant external bias and exposure conditions according to the curve 14 to 75 ° C does not fall below 90% and up to 120 ° C not below 75% of the room temperature value. The cause of the slight change is after the family of curves 15-17 in FIG. 6b, the parallel shift of the sensitivity curve to longer wavelengths can be seen. When changing from room temperature 25 ° C (curve 15) to an ambient temperature of 60 ° C (curve 16) or 74 ° C (curve 17), the edges of the sensitivity curves do not become flatter either. The results of earlier studies on the temperature dependence of the minority carrier lifetime in element semiconductors or compound semiconductors of elements of the 3rd and 5th group of the periodic system are relatively uniform.

From literature references for silicon, GaAs, AlGaAs, GaP and GaN it can be seen that the diffusion length L _p , L _n according to the equation L = L _Q Vexp (-E _a / kT) coincides with the activation energy E _a the temperature T changes when L _{0 represents} a scaling factor of the diffusion length. The activation energy fluctuates between 45 and 90 meV and the diffusion length increases accordingly with increasing temperature. In the case of indirect semiconductors made of VPE-n-GaP: S and LPE GaP: Mg, the lifespan increases both for measurements from the stored charge according to the blocking inertia method and for measurements of the decay of the photoluminescence. However, if the start, breeding, doping and cooling processes are changed (see DD-A 251 699 A3) and possibilities for the development of other types of point defects, for example in VPE-n-GaP: N highly doped with isoelectronic impurities , Te, the decay results may well be in contrast to the generally accepted trend. If deep acceptor-like traps with almost T-independent capture cross-sections act here, then the marked influence of temperature on the minority carrier lifetime disappears both with low and with high excitation densities. However, if the surface recombination determines the optical time behavior, then a faster decay at increasing temperature can be determined, especially at low excitation densities, if the light is preferably absorbed in the layers near the surface.

The measurements of the temperature dependence of the spectral sensitivity of the wavelength-selective photodiodes presented here do not indicate any drastic change in the service life of the minority charge carriers, in contrast to the experience of the experts to date. This means that there are no adverse consequences from temperature dependencies for the selectivity of the photoreceivers. The shift in the spectral curve is attributable to the temperature dependence of the bandgap of the semiconductor material. Accordingly, the service life of the minority charge carriers, despite their high temperature dependency, has not yet been able to increase to such an extent that the blocking filter function has waned or the short-wave or long-wave tails have been falsified by increased diffusion lengths compared to the constant layer thicknesses.

2nd embodiment

The second exemplary embodiment explains a photodiode in the near infrared range (1.0 to 1.7 μm). Narrow-band and wavelength-selective photodiodes are of interest here if, for example, different signal carrier waves are to be transmitted together via the same fiber, regardless of their propagation time differences, but are to be recorded separately. Ternary and quaternary mixed compound semiconductors of the InGaAsP system are suitable for such applications. The lattice constant of the selected mixed compound of In _! _ _x Ga _x As spans a relatively large range from 6.06 A for x = 0 of InAs to 5.65 A for x = 1 of GaAs compared to the AlGaAs system. The InP substrate chosen for this example is based on the coating results from GA Antypas (1972) on the GalnAsP alloy (published in the monograph: "GalnAsP Alloy semiconductors" by TP Pearsall published by John Wiley __ Sons Ltd. Chiehester, 1982 ) and according to R. Sankaran et. al. (published in the journal Journal Crystal Growth, 33 (1976), p. 271) with a lattice constant of 5.869 A. With defined x and y value pairs in the Ini _x Gaj -AS _y Pi- _y the lattice constant of the new layers to be formed can be set exactly to the substrate value, eg with the value pairs {x = 0.16 and y = 0.33}; {θ, 27 and 0.6} , {0.40 and 0.85} as well as {θ, 47 and 1.0} avoid any misalignment, which allows the concept of radiation absorption to be defined by pushing the absorption edge to 1.12 μm, 1.3 μm 1.55 Adjust μm or 1.65 μm as required.

[052] According to the invention, if the λ _M tuning is to be based on the definition of the minority carrier lifetime along the light path, this can be done by ignoring the grid-isometric conditions of the mixed compound semiconductor layers to be applied, on the one hand by using the ternary Ga _x Inι_ _x As and the gradation of the In proportion.

[053] A photodiode with a center wavelength λ _M of 1.3 μm, which is in demand in optical fiber communication technology, will now be described (FIGS. 7a, 7b, 8). For this purpose, a (100) -oriented, highly doped n-type InP (Sn or Te = 2 10 ¹⁸ cm ³ ) with a 3 μm di 27

Also cover n-type buffer layer 19 made of InP. A photoelectrically active layer 20 with a layer thickness of 2-5 μm is formed over it with the aid of the MO gas phase epitaxy. This epitaxial layer made of n-conducting Ini _x Ga _x As is tailored to the target wavelength and is set to an x value of 0.47 and thus to a grating constant of 5.869 A. As a result, the photoelectrically active layer 20 is well matched to the substrate 18. With its band gap of 0.73 eV, however, it is significantly narrower than that of the substrate 18 and the buffer layer 19 (band gap 1.35 eV). With a doping concentration of 4 10 ¹⁵ cm ³ in the photoelectrically active layer 20, the absorption coefficient is 1.2 10 ⁴ cm ^"1 at λ = 1.3 μm. The minority carrier lifetime here is greater than 10 ³ ns.

[054] The photoelectrically active layer 20 is now followed by a p-type, Zn-doped In ₁ _x Ga _x As epitaxial layer, the blocking filter layer 22, in order to form a pn junction 21. The barrier filter layer 22 is therefore provided with a larger x value than the photoelectrically active layer 20. The x value is now 0.65 and the barrier filter layer 22 is 7 μm thick. Near the pn junction, the doping concentration of the acceptors is evenly distributed at 5 10 ¹⁷ cm ³ . The frontal part of the barrier filter layer 22 is provided with a thin, very highly doped cover layer 23, in which the zinc doping was driven to 1.5-2 10 ¹⁹ cm ³ with a steeply falling profile by diffusion from external sources. Deviating from the minority carrier lifetime in the less doped barrier filter layer 20 with approximately 10ns, the minority carrier lifetime is reduced to 100 to 30 ps in the highly doped cover layer 23. All electron-hole pairs formed in the cover layer 23 by absorbed photons disappear immediately due to the short lifespan of the minority charge carriers.

[055] A limitation of the area of the pn junction 21 to 10 ^"4 cm ² per chip element for a small area photodiode is performed on the wafer by a conventional etching a mesa 24 (Fig. 8). All layer zones located on the substrate 18 to be approximately around the mesa 24 to the substrate 18. The slope of the mesa 24 has a small slope angle, so that the layers drawn over the slope pass from the mesa elevation to the substrate surface without cracks, for the direct incidence of scattered light via the slope into the photoelectric To suppress active layer 20, the embankment is covered with an opaque diaphragm 26. A component of this diaphragm 26 is a metal layer which makes a front contact 27 to the highly p-conducting barrier filter layer 22 and above an insulating layer 25 made of Si ₃ N ₄ partly via the Embankment of the mesa 24. The aperture 26 can be made by light-tight, non-conductive layer n Expand to the remaining front surface of the chip not occupied by the mesa 24. The front contact 27 is supplied with a defined blocking potential via a wire bridge 29 which is attached to a bond island 28. A back contact 30 is connected to ground potential.

LIST OF REFERENCE NUMBERS

Substrate buffer layer photoelectrically active layer barrier filter layer top layer anti-reflective layer front contact back contact crack (the band gap between the barrier filter layer 4 and the photoelectrically active layer 3) crack (the band gap between the photoelectrically active layer 3 and the buffer layer 2) profile part (doping profile in the p-conducting region) profile part (Doping profile in the n-type region) curve (photosensitivity of a wavelength-selective 74Onm photodiode) curve (temperature sensitivity of the photocurrent I _PH in relative units) curve (spectral sensitivity of the photocurrent at 25 ° C) curve (spectral sensitivity of the photocurrent at 60 ° C) curve ( Spectral sensitivity of the photocurrent at 74 ° C) substrate ((100) -oriented, highly doped n-conductive InP) buffer layer (made of n-conductive InP) photoelectrically active layer zone (made of n-conductive Inι_ _x Ga _x As with x value of 0.47) pn junction filter layer (p-type, Z n-doped Inι_ _x Ga _x As layer) Cover layer (thin, very high Zn-doped) Mesa insulating layer (made of Si ₃ N ₄ ) opaque panel front contact (to the high p-conductive filter layer; bond island wire bridge

Claims

claims

1. Wavelength-selective pn-transition photodiode made of ternary or quaternary III-V mixed compounds for a freely selectable, visible or infrared

Spectral region with a stacked arrangement of several functional zones normal to the direction of incidence of the electromagnetic spectrum, characterized in that to determine the sensitivity limits with regard to the detectable photon energy, a photoelectrically active layer (3, 20) and its layer positions on both surface sides of layers of different chemical composition abut, whereby on the irradiated side of the photoelectrically active layer (3, 20), a photoelectric blocking filter layer (4, 22) for short-wave radiation is formed from monolithically integrated semiconductor material, the energy band gap (E _GA (x)) of which is at least two components of the III-V -Mixed connection is set and a larger value than the energy band gap

(E _GB (x)) in the directly adjacent layer layers of the adjacent semiconductor material of the photoelectrically active layer (3, 20) and the minority charge carriers which are themselves optically generated by the

Design of the spatial course of the energy band structure and the expansion of the barrier filter layer (4) in connection with a suitable doping profile are prevented from reaching the adjacent photoelectrically active layer (3, 20) after contacting the barrier filter layer (4, 22) pn junction connects the photoelectrically active layer (3, 20), the semiconductor material of which is due to a large diffusion length of the optically generated minority Charge carrier excellent and in operation is detected by a space charge zone and the photoelectrically active layer (3, Tθ) by a heterojunction between a substrate (1) or a buffer layer lying over the substrate (1)

(2) and the photoelectrically active layer (3, 20) with a band discontinuity forming an access barrier (ΔB) for minority carriers from the substrate (1) in the course of the associated energy band, movable minority carriers in the latter

Do not follow minority carriers out of the substrate

(1) or the buffer layer (2) can get into the photoelectrically active layer (3, 20).

2. Photodiode according to claim 1, characterized in that in the barrier filter layer (4, 22) the energy band gap (E _GA (x)) is varied in layers in layers in the semiconductor material.

3. Photodiode according to claim 1, characterized in that in the barrier filter layer (4, 22) and in the photoelectrically active layer (3, 20) the energy band gaps (E _GA (x), E _GB (x)) in the semiconductor material in

Layer layers have a gradually varying course.

4. Photodiode according to claim 2 or 3, characterized in that the energy band gap (E _GB (x)) of the photoelectrically active layer (3, 20) on the exposed side has a smaller energy value than the energy band gap (E _GA (x)) Barrier filter layer (4, 22) on its irradiated side, but on the back in one Layer layer ends, which has a larger energy band gap than individual layer layers of the barrier filter layer (4, 22) and in connection with the heterojunction to the substrate (1) or an overlying buffer layer (2) the photoelectrically active layer

(3) with a band discontinuity forming an access barrier (ΔB) for minority carrier movement in the associated energy band.

5. Photodiode according to one of the preceding claims, characterized in that the layer thickness of the barrier filter layer (4, 22) is kept larger than the diffusion length of the minority charge carriers.

6. Photodiode according to one of the preceding claims, characterized in that the energy band gap (E _GB (x)) of the photoelectrically active layer (3, 20) has a greater value than the energy band gap (E _GS (x)) of the substrate (1) or the buffer layer (2).

7. Photodiode according to one of claims 1 to 5, characterized in that the energy band gap (E _GB (x)) of the photoelectrically active layer (3, 20) has a smaller value than the energy band gap (E _GS (x)) of the substrate ( 1) or the buffer layer (2) and the photodiode has two main surfaces that allow light to enter.

8. Photodiode according to claim 7, characterized in that in the heterojunction between the photoelectrically active

Layer (3, 20) and the substrate (1) or the buffer layer (2) the energy band gap to a constant The higher, higher energy value (E _GS ) than that of the energy band gap (E _GB (x)) of the photoelectrically active layer (3, 20) increases.

9. Photodiode according to claim 6, characterized in that in the heterojunction between the photoelectrically active layer (3, 20) and the substrate (1) or the buffer layer (2) the energy band gap to a constant, lower energy value (E _GS ) than that of

Energy band gap (E _GB (x)) of the photoelectrically active layer (3, 20) is reduced.

10. Photodiode according to one of the preceding claims, characterized in that the energy value of the band gap and / or the diffusion length in the barrier filter layer (4, 22) via the x value in the A _x Bι_ _x C _c D _d connection or the A _a BC _x Dx- _x connection is set, where A and B elements of the 3rd group and C and D elements of the 5th group of the periodic table and a, b, c and d do not vary from 0 to 1 constant values Components of the mixed connection are.

11. Photodiode according to one of the preceding claims, characterized in that in the barrier filter layer (4,22) from an Al _x Gaι_ _{x As} connection the aluminum content is set to a value between 0.05 and 0.4.

12. Photodiode according to one of claims 1 to 10, characterized in that in the barrier filter layer (4, 22) from an InGaAs _x Pι_ _x . -Connection the phosphorus fraction is set to a value which leads to the shortest diffusion length of the minority carrier lifetime.

13. Photodiode according to one of the preceding claims, characterized in that for the doping of the barrier filter layer (4, 22) with acceptors an acceptor type such as zinc, an epitaxial or diffusion process and a level of doping

N _A > 10 ¹⁷ cm ^{"3 is} selected and the diffusion length is reduced to values below 2 μm.

14. Photodiode according to one of claims 1 to 12, characterized in that for the doping of the barrier filter layer (4, 22) with donors a type such as tellurium, an epitaxial or diffusion process and a height of the doping N _D > 2 .10 ¹⁷ cm ^{"3 is} selected and the diffusion length is reduced to values below 2 μm.

15. Photodiode according to one of the preceding claims, characterized in that the barrier filter layer (4, 22) is completed by a cover layer (5, 23) with a high surface recombination speed.

16. Photodiode according to claim 15, characterized in that the cover layer (5, 23) is formed by a very high doping with a foreign atom type of the 2nd group of the periodic table, in which preferably acceptors such as zinc with a surface concentration of N _A > 10 ¹⁹ per cm ³ .

17. Photodiode according to one of the preceding claims, characterized in that the barrier filter layer (4, 22) has an electrical doping over its thickness such that under all electrical operating conditions of the photodiode Equipotential conditions exist or only a slightly varied electrical potential occurs in the direction of the light entry.

18. Photodiode according to one of the preceding claims, characterized in that in the semiconductor body between the barrier filter layer (4, 22) and the photoelectrically active layer (3, 20), a change of conductance from p- to n-type is arranged.

19. Photodiode according to one of claims 1 to 17, characterized in that in the semiconductor body between the barrier filter layer (4, 22) and the photoelectrically active layer (3,

20) a change of control type from the n to the p-line type is arranged.

20. Photodiode according to one of the preceding claims, characterized in that its light entry surface over the barrier filter layer (4, 22) is covered with an anti-reflective layer (6).

21. Photodiode according to one of the preceding claims, characterized in that the layer of high surface recombination is interrupted in a ring around the pn junction by pit-like etching or diffused protective rings.