DE2927183A1 - AVALANCHE PHOTODIOD - Google Patents

Description

R.Dorn-K.Lösch 1-1

kvu ranc he-Phot od iode. .

The invention relates to Avalanehe photodiodes such as, for example, Receivers can be used in optical communications technology.

They are mainly avalanche photodiodes made from element semiconductors Silicon, and from compound semiconductors or semiconductor alloys known.

Basic designs for silicon avalanche photodiodes are described in the article by. f'JLJ Bollen et al: "Die Avalanche-Fotodiode", Philips techn, Rdsch. 36, 220-226, 1976/77, No. J, pages 220-226, ". The zone in which the amplification of the minority charge carriers, i.e. the avalanche effect, takes place, is formed by an n- and a p-doped silicon layer. Instead of a pn junction, a metal-semiconductor junction with blocking characteristics can of course also be used. Since the silicon absorbed (gain region), especially at conventional transmitter wavelengths of about 1 to not more strongly, even a relatively thick tr -doped SiIixiumschicht is added to the gain region, soft z \ x OINC-m essential part of the eindririß'-nde radiation abaoi · biert (absorption layer). In one embodiment, which is described in the article by A. Atamann and J. Müller, "Double-meaa reach-through avalanche photo-.liudes with a largo gain-bandwidth product made from thin silicon filmr.", J. Appl. Phya. - V) (10), Oct. 1978, pages 5324-5331, thicknesses of the ρ and η range in the reinforcement are from 0.2 to 0.3y.irii, on the other hand thickness ¹ ! stated by ^r .- ?. O jim of the absorption ouhicht.

Dr. J / Sam
June 27, 1979

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As the mentioned article in Phi Lips techn. Rundsehmj shows the ratio of the ionization coefficients of holes and electrons in the semiconductor base material used. The more this ratio differs from one, the lower-noise amplification is possible. The ratios given in the literature are, for example, for Si ^ 5, for Ge 0.5 (H. Melchior; J. Lui'iluv. ·;.:.: “Sensitive High Sp ^ ed Photodetector: -} i'c> r the Demodulation of Visible and ivrar Infrared Light ", 7 (lJ73), 3 ^r J0- ^ l ^ i), for Ga _{n t} . _r , In, - -, As 0 (TP Pearsall and N. Papuchon" The Ga _n u _r . In-, _r; -. Homo j unction Photodiode - A New Avalanche Photodetector in the near Infrared between 1.0 and 1.6 JIm ", Appl. Pliya. Lett.; i3 (Y), 1 Oct. 1973, Rare 640-642).

As can be seen from the cited literatures, silicon has the best reinforcement communities of the semiconductor base materials known to date. Since silicon no longer absorbs at wavelengths of, for example, 1.2 odor 1.6 μm, at which the glass fibers used in optical communications technology have attenuation minima, numerous working groups have endeavored to find avalanche diodes on dt-ν Hau in von Verb Lndungal : to develop semiconductor and semiconductor alloys that should have good absorption and good reinforcement properties.

The work by Pearsall et al. in Appl. Phys. Lett, has already been mentioned. In this and in other works such as that of TF Lee et al .: "In Πι, As P / In P Photodiode. * ;: Micropia Lima -Limited Avalanche Multiplication at 1-1 ο um Wavelength", IEEE J. Qu. E.g., Vol.QE-IS, fJo. 1, Jan 1979, Seitii-n 30 to '5 ¹ J, will address the difficulties of this new

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Avalanche photodiodes in relation to dark currents and microplasmadur breakages received.

The object of the invention is to provide an avalanche photodiode with a reinforcement zone consisting of a pn junction or üineiTi metal-semiconductor ubex'gang with blocking characteristic, furthermore with a semiconductor applied to the reinforcement zone as an absorption layer ter'ücliielit, in which the largest ΤοΓΓ of the total of the Diode absorbed radiation is absorbed, 'to train that with "the best possible absorption properties good amplification without. Problems related to microplasrna charges can be achieved. . . ■

The solution to the problem is that in a generic Avalanehe photodiode for amplification a & orie (1) a semiconductor base material is used, which -as possible_ has good reinforcement properties and that for the absorption layer (2) a semiconductor base material is used which absorbs as strongly as possible at the wavelengths at which the diode is to be operated, and that. the Conductivity type of the semiconductor of the absorption layer matches with the conductivity type of the semiconductor region of the reinforcement zone followed by the absorption layer.

As already mentioned, e.g. silicon is a material which has excellent reinforcement properties. It allows high amplification with little additional noise. on a layer of a semiconductor with good gain properties is a layer of a highly absorbing semiconductor upset. Which semiconductor gruride materials are embossed for which wavelength to be absorbed is Tables can be easily taken from the extensive literature.

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R.D ^ rn-K.Lösch l-i

The advantages, namely the best possible amplification / reigenßchafteri paired with the best possible absorption properties On the hand. Advantageous further education and training forms are given by the (Jntoi'an; ". prüche.

This can result in fault currents due to charge carrier recombination lattice defects or microplasma breakthroughs a.B. by customizing of the lattice constants of the different semiconductors - layers reduced b: -: w. selected> a; .- <- n be.

A further version enables you to work with high field strengths work in the Vei'BtfJi'kunßLiSoue su and the field strength to keep it low in the absorption layer. This results in a polycrystalline or amorphous design, for example the absorption layer allows.

If a semiconductor base material is chosen for the reinforcement zone, which has very few catallographic defects contains, it is possible to work at particularly high field strengths without microplasma breakthroughs occurring.

The invention is illustrated below with reference to embodiments and the figures in more detail. Show it:

1 avalanche photodiode with a structure according to the invention. FIG. 2 field strength distribution in a diode according to FIG. 1

Fig. 3 field strength distribution in an improved embodiment such an Avalanehe photodiode

Fig. '\ Building a Avalanehe photodiode having a field profile of Figure ¹ 3

5 shows an avalanche photodiode according to the invention in section

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In 1 ' ¹ IPjUr 1 there is a successor A vi! . ^! iricho-i'tr> t -> d io.ien structure shown. . The structure comprises a reinforcement zone 1 consisting of two semiconductor areas of different conductivity types, an absorption layer 2 consisting of a metallic conductor loop, so that contacts 3 In the embodiment shown, the radiation preferably enters the diode from the side of the reinforcement zone . This is shown in the picture by the arrow *

The reinforcement zone consists of a basic semiconductor material that has particularly good reinforcement properties. Tm at up ic! 1 vmrde chosen for this silicon. In silicon the ionization coefficients for electrons are up to ΊΟ i times above that for Loohei ¹ . This ratio, which deviates significantly from one, results in a high gain with little noise, as can be seen from the Philips Techn. Rundschau article. The relatively large Bandlür-.ko in silicon results in low thermal dark currents, which also has a positive effect on the noise level of the amplifier. Furthermore, silicon is the one «. Semiconductor basic dimensions that can be herntelJon in the best Kinkriatallqualltät, ie with the lowest number of kr-istallographischen errors. As a result, knowing Im oilisiuin very hoiit, -! '' Were built without local breakthroughs (microplium breakthroughs) occurring te r-ri? ir --'- £ i or quat f-rn'iron tktlbleiter, often use the local DurchDrüeho before the avalanche affliction in the volume (see - / ,. ti. dfi, ζ Ltierten article by Lee et al ).

Jn practice widespread, is a u r. Transition in silicon, as it is in the example flor- Figure 1 arigeg ^ bfn-. "Instead of de. ^

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; i; t LL-lei ¹ ei-transition is -.- j of course; it is also possible to work with a semiconductor metal transition with blocking characteristics "u. A question here is; _: ; .B. a p-Si liziura-Go Id transition.

I.n'.e Absorptionssehicht 2 in Figure 1 bestent of Ga, .., in., As a absorpt which lonsniax imum at about I, u2 up to

O ι > 1

white, ie as an absorption material i. "äc the length of l, b µm used in the optical fjaehrichr enter h:; ik is very well suited. -; orpf, ionssch i .ent choose a semiconductor whose band gap is equal to or slightly smaller than the energy of the quanta of the received radiation, [read follows directly from the absorption mechanism of the semiconductor.

In the exemplary embodiment, aas Oa ,, ₇ In. _{[: r} As very slightly p-doped, with an acseptor density of approx. 10 ^J Z η / cm ( if semiconductors). This weak doping is fermented avalanche photodiode technology. Eolle-n et al in Ph i. 1 i ps Techn. Rundschau}.

The ohmic contacts "5 are made of vapor-deposited Au-Ti on; '. I 1 i'-, ium b: -; w. Made of Au-in-Ti on the Ga, ,, .-, iri_. _ΓΎ As; daU.-i i.it the {- [ontacting also i-aing technology.

At shorter wavelengths, of lier Lanalücke from absorbier-eii vij.o · semiconductors exceeded ei η wide margin. For all wavelengths that can be used for optical transmission technology, i.e. from cn. 1.-1.6 um comes in: also 'Jerrnard-iiin al., Very good absorption m.ti "eria 1 in question. It can be like oil i :; ium in the highest- kr: sta I iogr-.phis-' ru r quality produced; ■ · .tr · 1.1 r, are and can auP.er'aem through Oo-üi intermediate layers

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good in its lattice constants; to be adapted by Mi. This avoids lattice defects at the transition layer between Ge and Si, which always lead to leakage currents due to charge carrier recombination and local breakdowns at high field strengths r, u. The lattice constant of Si is 5 ₃ 3 ^ λ ", that of Ge 5, C6 K. Such a Ge-Si alloy semiconductor layer can also be used as an absorption layer.

Figure 2 shows se nematically the field strength curve in a -. . Diode structure according to Figure 1. The highest field strength is at the pn junction. Different field strengths are entered on the ordinate, namely Ey ₃ E ^, E „. The desired amplification takes place in the field strength range of the diode in which the field strength is approximately E _v and greater than E ". Ey. on the other hand, is a medium field strength at which microplasma breakthroughs occur as a result of local field increases at crystal disturbances. A semiconductor base material is only suitable as a material for the amplification zone if it can be produced in such good quality that no local breakdowns occur ^before the onset of amplification at the field strength Ky . Ε ~ is the field strength at which free charge carriers have saturation drift speed. The field strengths are different in the absorption layer 1 and in the reinforcement zone 2 and are identified in FIGS. 2 and 3 with the indices 1 and 2.

Prerequisite for low-noise operation of the avalanche photodiode is that not microplasma breakthroughs at a field strength E _M <E _y prevent reaching _seven, the field strength E. If the crystalline high quality Si is used, this is easy to achieve for the amplification area.

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As is shown in Figure 2 , the course is very steep in the Veratärkungsbereich. This leads to the fact that crystal disturbances, which have an effect from the interface area of the absorption layer / reinforcement area in the latter area, slightly cause additional field strength increases, which have the consequence that the field strength for microplasma breakthroughs is reached locally in the amplification area.

liin another disadvantage ac- ;; Field strength curve s according to FIG. 2 consists in the fact that in the absorption layer the field strength Ep sum part necessary to achieve the saturation drift velocity is considerably exceeded and undercut. It would be ideal to keep about the field strength Ej :: u over the Gaussian angle.

Both disadvantages. ¹ are eliminated by a field strength curve according to FIG. Between the reinforcement area 1 and the absorption layer 2, a zone I made of the semiconductor base material of the reinforcement but of the conductivity type of the absorption layer with weak doping is inserted. This zone ensures that crystal disturbances which develop due to a lattice mismatch between the semiconductor base materials of the absorption layer or the reinforcement zone and the inserted zone 4 can no longer affect the reinforcement zones. Therefore, even polycrystalline or amorphous material can be used for the absorption slide.

Furthermore, there is a highly doped layer on the absorption layer 2 Zone 5 connected to the conductivity type of the absorption layer. This zone enables the field strength in the entire absorption layer to be greater than or equal to the sum the saturation drift velocity necessary

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R.Dorn-K.Lösch 1-1

Field strength E, ■■ au ha Jt en and-the field strength _ t-rst in zone 5 to be reduced to zero. This measure is ?,. B, in an article by Bollen et al. in Philips .Techri. Roughly described. If this highly doped Zane 5 is made of a semiconductor base material which does not absorb the incident radiation, radiation can be made through this layer into the absorption layer. _{In the case of Ga 1} , "In. As as absorbing material, for example InP" would be considered as the semiconductor base material for this Swreck. A modified stratification sequence based on FIG. 1 would be, for example, η SipSi, T) -Si, VQa, _ In As ₅ ρ InP.

An exemplary embodiment is shown in FIG. the Reinforcement zone "1 consists of" η and pSi to which a Field strength-reducing TTSi zone 4 is connected. The absorption layer 2, made of TT-Ge, closes with a highly doped one ρ Ge zone 5. The «contacts 3 are brought about by vapor-deposited Au-Ti contacts.

FIG. 5 shows a section through an avalanohe photodiode according to the invention, the production of which is described below. The starting point is an ihSi. Substrate into which a ρ and an η layer is diffused using the method described in the work by Atamari..et al. In J. Appl. Phys. is described. The ρ Yi ¹ ZMi. η Si areas are 0.2-0 .mu.m thick. After diffusion, an Au-Ti layer for ohmic contact is vapor-deposited, but with a "window" 6, ie, an Au-Ti-free zone above the pn junction, through which radiation is then emitted in the case of a finished diode The treated substrate is soldered onto a gold base which has a hole through which the radiation S can dig into the diode.

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tiri / 'JhnT.en Arl> it ber-'chr K benen . In the next work cycle, the JfS i substrate 1: i aur approx. 5 um L-ie Iu-? abät-i-.

Made of so far? Diode will only; rider applied the absorption layer. This happens sB by gas phase epitaxy or by; h melting of W -CiOr'maniiim. D per layer thickness of the germanium häru'jt von dei ' to. absox'bier-ending wavelength. p.ei 1,2 ^ in VJeI I.enl'iri ^ e iat the germanium layer thickness approx. 1, ^ - 2 | im, Lei l, i> ^ trn wavelength approx. 10 jliiu. In the JT Germanic layer, the upper ρ Ge layer t '-: eu :: t .. A concluding statement; vex'lc-iht on it the Diou,: lie usual, advantageous mesa shape. The co-operation is again achieved by vapor-deposited Au-Ti.

The diode is for irradiation through the gain zone intended. This is possible with practically no losses, since the amplification sound as a result of the higher level present there The edge spacing is transparent for radiation with wavelengths longer than 1.1.

Radiation into the absorption layer from the side is special then advantageous if very long wavelengths are to be received, bt.-i those in common semiconductors only " still very weak '.- absorption at.ittfind ..: t. Through the side Irradiation is equal to the "effective absorption length the lateral expansion of the absorption layer and not equal to the layer thickness and can therefore be made very large without the drift: 'since the charge carrier' increases, as would be the case if the layer thickness were increased.

In the case of structures other than the one described here, it can see as necessary erv / t-. isen, the junction of the To provide the strengthening zone with a groove and ring structure,

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uiii Mii \ .ropiäi> m; -iJurcliLrüche und Handflanh ^ nitro tones in aen itond-. Avoid transition 211 ions. However, these are for the various embodiments of the transition zones known technical means.

The semiconductor layers consist either of element semiconductors, for example Ge or Si, or of compound semiconductors, aB. Ga As, InP or Cu In Se ₉ , etc., or alloy semiconductors, KB Ga _1- In As or Ga _1- In ₁ As ₁ P; . Before-

- "J." * "XX XX IX J. y _t y _

the layers are preferably monocrystalline and, above all, in The reinforcement zone is of the highest quality. The absorbent Layer can, however, be used to lower the field strength Zone between reinforcement zone and absorption layer also be polycrystalline or amorphous.

In FIG. 3 and when explaining the function of the heavily doped zone 5, it has already been shown that this is caused by the reverse voltage caused field entirely through the absorption layer 2 engages. This is especially necessary when diodes with fast switching behavior are to be achieved. For that should in the whole absorption layer the field strength be so great, that everywhere through the prevailing field the saturation drift velocity the load carrier is reached.

Analogous to what has been described so far, it goes without saying also possible instead of a semiconductor base material as an absorber layer to arrange several semiconductor base materials next to each other as absorption layers, the different Absorb wavelengths.

The diodes according to the invention can not only be used in independent components but also in integrated circuits, e.g. on Si, GaAs or InP-based use can be found. By applying various Semiconductor base materials as an absorption layer at different points of gain zones of the integrated circuit, the integrated circuit for different wavelengths to be received are made sensitive.

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Claims (1)

STANDARD ELECTRICS LORENZ
Aktiengesellschaft Stuttgart R.Dorn-K.Lösch 1-1 Avalanche photodiode Patent claims : (Iy avalanche photodiode with an amplification zone, consisting of a pn junction or a metal-semiconductor junction with blocking characteristic, furthermore with a semiconductor layer applied to the semiconductor of the amplification zone as an absorption layer, in which most of the radiation absorbed by the diode is absorbed, characterized in that a semiconductor base material is used for the reinforcement zone (1) which has the best possible reinforcement properties and that a semiconductor base material is used for the absorption layer (2) which is as strong as possible at the wavelengths at which the diode is to be operated absorbed, and that the conductivity type of the semiconductor of the absorption layer corresponds to the conductivity type of the semiconductor region of the reinforcement zone, which is followed by the absorption layer. 2) avalanche photodiode according to claim 1, characterized in that the semiconductor base material Dr. J / Sam -. - ./. June 27, 1979. 030062/0515 29271S3 R.Dorn-K.Lösch 1-1 the reinforcement zone (1) has very different ionization coefficients for electrons and holes . 3) avalanche photodiode according to claim 2, characterized gekennz eichnet that the semiconductor base material is GaAs or InP or GaSb or an alloy of these materials or silicon. ^; l) avalanche photodiode according to one of claims 1 to 3, characterized in that the semiconductor base material of the absorption layer (2) has a gap which is less than or equal to the energy of the quanta of the received radiation. 5) avalanche photodiode according to one of claims 1 to ^L \ , characterized in that the semiconductor base material of the absorption layer _{(2) germanium or Ga 1} ^ In _x As ₁ P _y or Ga ₁ In, As or Ga. Al As ₁ Sh _r or GaAs _1- Sb or CuInSo ₉ χ ~~ χ x - ι —x xxyy ι χ χ ^ 6) avalanche photodiode according to one of claims 1 to 5, characterized in that the semiconductor base materials of the absorption layer (2) and reinforcement zone Ci) are matched as precisely as possible in their lattice constants. 7) avalanche photodiode according to claim 6, dad u rch geke is used to mark, that the use of Si and Ge, the lattice constants of Si-Ge transition layers are adapted to each other. 3) avalanche photodiode according to one of claims 1 to 7, characterized in that a zone (H) between the reinforcement zone (1) and the absorption layer (2) 030062/0515 R.Dorn-K.Lösch 1-1 which consists of the semiconductor base material of the reinforcement son, has the conductivity type of the semiconductor of the absorption zone, but is less doped ( ir or V - semiconductor). 9) avalanche photodiode according to one of claims 1 to 8, characterized in that the semiconductor of the absorption layer (2) is lightly doped and that on its side facing away from the amplification zone (1) a zone (5) of high doping of the same conductivity type is attached . 10) Ävalanche photodiode according to claim 9, characterized in that the highly doped zone (5) does not absorb at the wavelengths at which the diode is to be operated. 11) Ävalanche photodiode according to one of claims 1 to 10, characterized in that the diode is used for irradiation through the gain zone (1). 12) avalanche photodiode according to one of claims 1 to 10, characterized in that the diode is used for irradiation from the side. 13) avalanche photodiode according to claim 10, characterized in that the diode is used for radiation through the highly doped zone (5). 14) avalanche photodiode according to one of claims 1 to 13, characterized in that the semiconductors are element semiconductors or compound semiconductors or alloys of such semiconductors. 030062/0515 ORiGiHAL R.Dopn-K.Lösch 1-1 1 * 5) Avalanehe photodiode according to one of .Ansprüche 1 to 1- ¹ I _3, characterized in that the semiconductor of the amplification zone (1) as little as possible; contains crystallographic errors. 16) Avalanehe photodiode according to one of claims 1 to 15, characterized by ₃ that the semiconductors are a ^ krietailin. J7) avalanche photodiode Nicli no egg of claims 1 to 15, h rc dadu ₃ in that uie absorbent layer (2) polycrystalline or amorphous. 18) Avalanche photodiode according to one of claims 1 to 17, characterized in that the amplification zone (1) is stranded with a Schutsringstruktur. 19) avalanche photodiode according to any one of claims 1 to 18, dad urch terized in that the absorption layer (2) is doped so that when applied reverse voltage, the resulting field reaches through the entire Absorptionssehieht. 20) avalanche photodiode according to any one of claims 1 to 19, characterized g ekennzeic h net that several different semiconductor base materials are applied as Absorptiorisschichten side by side on the reinforcement zone (1). 21) avalanche photodiode according to one of claims 1 to 2O _3, characterized in that the diode is used in integrated circuits. 030062/0515 BAD ORfGiNAL