0.9 ev POTENTIAL BARRIER SCHOTTKY DIODE ON ev GAP GaxIn1-xASSi:H

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1 0.9 ev POTENTIAL BARRIER SCHOTTKY DIODE ON ev GAP GaxIn1-xASSi:H A. Deneuville, F. Valentin, S. Belkouch To cite this version: A. Deneuville, F. Valentin, S. Belkouch. 0.9 ev POTENTIAL BARRIER SCHOTTKY DIODE ON ev GAP GaxIn1-xASSi:H. Journal de Physique Colloques, 1988, 49 (C4), pp.c4-449-c < /jphyscol: >. <jpa > HAL Id: jpa Submitted on 1 Jan 1988 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 Colloque C4, supplément au n 9. Tome 49, septembre 1988 C*-H9 0.9 ev POTENTIAL BARRIER SCHOTTKY DIODE ON ev GAP Ga x In x. x AS\a-Si:H\Pt A. DENEUVILLE, F. VALENTIN and S. BELKOUCH Laboratoire d'etudes des Propriétés Electroniques des Solides, CNRS, BP 166, F Grenoble Cedex, France, Associated with Vniversity Joseph Fourier, Grenoble, France Résumé - Les courbes I(V,T) de ces structures pour 1000 Â de a-si:h et x = 0.2 et 0.47 sont similaires à celles des diodes Pt/a-Si:H et en conséquence contrôlées par l'interface Pt/a-Si:H. Ceci ouvre de nouvelles perspectives pour les MESFET sur Ga x Ini. x As. Abstract - The I(V,T) curves of such structures for 1000 A of a-si:h and x = 0.2 and 0.47 are both similar to those of Pt/a-Si:H diodes, so controlled by the Pt/a-Si:H interface. This opens new perspectives for MESFET on Ga x Ini. x As. 1 - INTRODUCTION The transmission wavelengths of optical fibers fit the gap of Gao.47Ino.53As (0.75 ev) or Gao.2Ino.8As (0.5 ev). Integrated circuits with detection and treatment of the photoinduced current are wished. At this moment neither MISFET nor MESFET structures are satisfactory respectively from problems to prepare good insulators on III-V semiconductors and from the pinning of the Fermi level at the metal HI-V interface very close to the conduction band edge. Loualiche et al HI have shown that a 0.78 ev potential barrier can be obtained with the structure Gao.47lno.53As\a-Si:H(1000 A)\Pt. The aim of this work is to reproduce this result, to improve the performance of the structure and to check if it works also on the 0.5 ev gap semiconductor Gao.2lno.8 As of the same family. 2 - PREPARATION AND APPARATUS The Ga x Inj.. x As films grown by MBE on semi-insulating InP are supplied by Loualiche of CNET Lannion. The a-si:h films (1000 A) are deposited by glow discharge decomposition of SilLj in SiH4 10 %/H2 90 % mixture at a total pressure of 1.9 Torr and 230 C on the Ga x Ini- x As and also on high resistivity Si monocristal for physicochemical characterisation. This is mainly done from the analysis of its infrared absorption by a Perkin Elmer 683 Infrared Spectrophotometer. The height of the potential barrier is derived from the analysis of the I(V,T) characteristic which is recorded from 200 to 400 K by a Keithley 617 electrometer controlled by a microcomputer Apple II. 3 - EXPERIMENTAL RESULTS AND DISCUSSION The a-si:h is an amorphous wide band gap (~ 1.8 ev) semiconductor whose properties depends mainly on the hydrogen content. At low thicknesses, oxygen can also be included in the film which damages its properties. Hydrogen content as well as oxygen contamination of a-si:h film can be studied through the specific absorption bands of Si-H and Si-O bonds. There are several absorption bands according to the mode of vibration of the bond. We check here the wagging mode of the Si:H bond around 630 cm" 1 and the stretching mode of the Si-O.bond around ~ 1050 cm -1. Their oscillator strength is constant 121, I'M, which allows a derivation of the H and O concentration from the area of the absorption bands after calibration. For instance, the I-R absorption band for the 1000 A a-si:h film is given on Fig. 1. From the aera of the 630 and 1050 cm -1 bands we deduce an hydrogen content of ~ 28 % and an oxygen contamination of ~ 0.2 %. The hydrogen content is as usually higher than in thick films, the oxygen contamination is at a quite satisfactory low level. Article published online by EDP Sciences and available at

3 WAVE NUMB!3! icm-lj Fig. 1 - A typical infrared absorption curve for 1000 A of a-si:h deposited at 230' C by a 50 khz glow discharge. The I(V,T) curves of both the Ga0.47Ino.53As and Gag.2Ino.gAs structrues exhibit a Schottky behaviour as shown respectively on Fig. 2 and 3. In both cases, the current density increases from A/cm2 to A/cm2, and the ideality factor n decreases from 1.6 down to 1.1 as the temperature increases. There is also for both structures an inactivated current component appearing below K and whose relative intensity increases as the temperature decreases. This may be tentatively attributed to a tunnel component through the localized levels of a-si:h V0LT;tGE Fig. 2 - The I(V,T) curves of a Pt\a-Si:H\Gw.47Ino.53As structure.

4 VOLTAGE (V) Fig. 3 - The I (V,T) curves of a Pt/a-Si:H/Gao.2Ino.8As structure. From the extrapolation of the linear part of the forward characteristic to zero voltage, we deduce the saturation density of current at each temperature. It is thermally activated, with respectively 0.94 ev (Fig. 4) and 0.84 ev for the Gao.47In0.53As and Gao.2Ino.8As structures. Ja W1000~ a-sihigao,47 In0,53 ;is I k. \ 9,Q , I I I l Fig. 4 - The saturation current Js versus the reciprocal temperature for the Ptfa-Si:WGa0.471no.53As structure. \,O, > 2' 2E LO,or,?,gui/T

5 [ exp & - 1 ] as for the usual Schottky So the I(V) curves of these structures can be represented by J = A enp - diode, except that as for Metal/a-Si:H /4/ diode we cannot choice between a diffusion or thermoionic behaviour for the saturation current. The ideality factor and the saturation current are higher and the potential barrier slightly lower for the x = 0.2 than for the x = 0.4'7 structure. If we compare to the results of Loualiche et a1 /I/ for x = 0.47 we get here at room temperature n = 1.2 instead of n = 2 Js A/cm2 instead of 10-7 A/cm2, q@b ev instead of 0.78 ev for the same a-si:h thickness of 1000 A. for x = 0.2, n = 1.35 Js ~/cm2 and q0~ ev. So, the structures have been improved in regard to the previous ones (lower n and Js, higher qab)and the results are similar for x = 0.2 and The ideality factor, current density and potential barrier obtained here are also similar to those of Metalfa-Si:H Schottky diodes. So, this suggests, that the I(V,T) curves of this kind of structure are mainly controlled by the Metalfa-Si:H interface, which is confirmed by measurement on the same type of structure with various cristalline semiconductors 151. CONCLUSION We have shown that Schottky type structures Pt/a-Si:H/GaxInl-xAs (x = 0.2 and 0.47) can be obtained for 1000 A of a-si:h with good ideality factors, low saturation currents high potential barriers, significantly improved in regard to the previous results on x = 0.47, similar to those of Pt/a-Si:H diodes. These caracteristics are controlled by the Pt/a-Si:H interface, and so, the potential barrier 0.9 ev is much higher than that of Pt/Ca,In~.,As (I 0.3 ev) which will considerably help for MESFET structures. REFERENCES /I/ S. Loualiche, C. Vaudry, L. Henry, A. Le Cone, Electronics Letters 22, (1986), 897. /2/ H, Shanks, C.J. Fang, L. Ley, M. Cardona, F.J. Demond, S. Kalbitzer, Phys. Stat. Sol.(b) 100, (1980), E. C. Freeman, W. Paul, Phys. Rev. B 20 (1979) A. Deneuville, M.IH. Brodsky, J. Appl. Phys. 50 (1979), A. Deneuville, E. Gheeraert, S. Belkouch, unpublished.