Degradation of Hydrogen-Passivated p -Type Layers in GaAs by Minority Carrier Injection and Reverse Bias Annealing
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DEGRADATION OF HYDROGEN-PASSIVATED p-TYPE LAYERS IN GaAs BY MINORITY CARRIER INJECTION AND REVERSE BIAS ANNEALING A. J. TAVENDALE*, S. J. PEARTON**, A. A. WILLIAMS* AND D. ALEXIEV* *ANSTO Lucas Heights Research Labs, Menai NSW Australia **AT&T Bell Laboratories, Murray Hill, NJ 07974 ABSTRACT We detail experiments showing that acceptor passivation by atomic hydrogen in p-type GaAs is unstable to either illumination, forward bias annealing or reverse bias annealing. The long-term stability of operation of devices employing hydrogen in or near the active region of FETs or quantum-well lasers is therefore questionable. The systematics of acceptor reactivation during minority carrier injection or reverse bias annealing are presented. INTRODUCTION The passivation (or neutralization) of electrical activity of shallow dopant impurity and deep level centers in GaAs is currently a topic of considerable theoretical and practical interest, and has been 2 the subject of a number of recent reviews.il' 1 Applications of hydrogenation have already been extended to the engineering of GaAs field effect transistors[3' and AIGaAs-GaAs quantum well laser devicest41 indicating the potential technological importance of the technique. In these instances the atomic hydrogen was injected by diffusion from a plasma source. 5 It has been previously reported by usl l and confirmed by others that hydrogen may be electrotransported as H' in the reverse bias depletion layers of Al Schottky or n'p junction diodes on hydrogenated p-type Si. Further, we have reported that under conditions of minority carrier, acceptor neutralization in such structures is unstable. No similar study has been reported for hydrogen in pGaAs. Such phenomenon could prove useful in device engineering and crucial in the long-term stability of operation.
The purpose of this paper is to report electrical (C-V) and SIMS profiling measurements of reverse-bias annealed Schottky diodes from hydrogenated p-GaAs which demonstrate the existence of mobile H', together with minority carrier injection annealing analogous to the behavior of hydrogen in Si. It is well established that hydrogen has a deep donor state in p-type Sit2,51 and there is some t evidence that it may also have an acceptor state in n-type material. 61The situation for hydrogen in Ill-V semiconductors is much less clear. The fact that a counter-doped, n-type layer on p-type GaAs inhibits the indiffusion of hydrogen from a plasma source has been postulated as being consistent with hydrogen having a donor level in the upper half of the band gap of GaAs.[71 To this point however, there has been no direct evidence for the charge states of hydrogen in any compound semiconductor. This is one of the key remaining issues for these materials, since the diffusion kinetics and donor and acceptor passivation mechanisms have been closely studied in recent times.[8- 111 In this letter we report direct evidence for the existence of a positively charged hydrogen species in GaAs by monitoring its motion in the depletion region of
