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Submitted on 1 Jan 1988
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0.9 eV POTENTIAL BARRIER SCHOTTKY DIODE ON 0.75-0.5 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 0.75-0.5 eV GAP GaxIn1-xASSi:H. Journal de Physique Colloques, 1988, 49 (C4), pp.C4-449-C4-452.
�10.1051/jphyscol:1988495�. �jpa-00227993�
0.9 eV POTENTIAL BARRIER SCHOTTKY DIODE ON 0.75-0.5 eV GAP GaxInx . 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-38042 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 GaxIni.xAs.
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 GaxIni.xAs.
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 GaxInj..xAs 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 GaxIni-xAs 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 http://dx.doi.org/10.1051/jphyscol:1988495
JOURNAL DE PHYSIQUE
WAVE NUMB!3! iCm-lj
Fig. 1
-
A typical infrared absorption curve for 1000A
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
-
10-11A/cm2 to-
10-4A/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-
260 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:HV0LT;tGE
Fig. 2
-
The I(V,T) curves of a Pt\a-Si:H\Gw.47Ino.53As structure.Fig. 4
-
The saturation current Js versus the reciprocal temperature for the Ptfa-Si:WGa0.471no.53As 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
W 1 0 0 0 ~ a-SiHiGaO,47 In0,53 ;is
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\.
\.
k.
\ 9I
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\. -
\.
1 , I I I l
\.
\ , O
,
>2' 2E 3.2 2.6 LO
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,gui/T
JOURNAL DE PHYSIQUE
So the I(V) curves of these structures can be represented by J = A enp -
[
exp& -
1]
as for the usual Schottky 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
-
10-10 A/cm2 instead of 10-7 A/cm2, q@B-
0.9 eV instead of 0.78 eV for the same a-Si:H thickness of 1000A.
for x = 0.2, n = 1.35 Js
-
10-10 ~ / c m 2 and q 0 ~ 3-
0.84 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 0.47. 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), 43.
131 E. C. Freeman, W. Paul, Phys. Rev. B 20 (1979) 716.
141 A. Deneuville, M.IH. Brodsky, J. Appl. Phys. 50 (1979), 1414.
151 A. Deneuville, E. Gheeraert, S. Belkouch, unpublished.
