Passivation of Surface and Bulk Defects in InP
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PASSIVATION OF SURFACE AND BULK DEFECTS IN InP SATHYA BALASUBRAVNIAN VIKRAM KUMAR*, N. BALASUBRAMANIAN AND V. PREMACHANDRAN * Department of Physics, Indian Institute of Science, Bangalore 560012, India. ** Microelectronics Laboratory, Indian Telephone Industries, Bangalore 560 016, India ABSTRACT The effect of sulfur and hydrogen plasma treatment on the Schottky barrier and photoluminescence (PL) properties of p-InP is reported. Both the treatments increase the barrier height of Au/p-InP diodes and band to band PL. This is explained as being due to a shift in the surface fermi level position towards the P vacancy related pinning level in the top half of the band gap. The H+ treatment passivates the shallow and deep levels as observed from the C-V depth profile and PL respectively. Passivation of defects at the surface and in the bulk of compound semiconductors has attracted considerable attention in the recent past. The surface of most of the III-V compounds has a large surface state density which pins the fermi level in the bandgap. The large surface state density results in a large surface recombination velocity which is detrimental in most of the device applications. On the other hand, the deep levels in the bulk have their own merits and demerits depending upon the application. Many of the deep levels in semiconductors are process induced and sometimes it is necessary to suppress their effects. The surface passivation of GaAs has been effected using a sulfide solution treatment [1,2]. An enhanced room temperature photoluminescence (PL) after a treatment with sodium sulfide or ammonium sulfide has been observed [2]. This has been attributed to a reduction in surface state density and hence the surface recombination velocity. But Spindt and Spicer [31 argue on the basis of a two level defect model that the increase in PL is due to the shift in the fermi level pinning position from the midgap donor states to the acceptor states near the valence band maximum after the sulfide treatment. Carpenter et al. [4] have reported that upon sulfide treatment of n and p GaAs, the surface state density reduces such that the Schottky barrier height is more sensitive to the metal work function. Similar observation has been made on n-InP [5]. No such report for p-InP is available at present. Recently surface "passivation' effect has been observed as an enhancement in band to band PL in the hydrogen plasma treated GaAs [6]. It is known for quite some time that hydrogen plasma treatment results in passivation of shallow as well as deep levels in the bulk [7,81. In the case of InP, hydrogen passivates shallow Zn [8,9] and Cd [9] acceptors. Swaminathan et al. [9] have observed a complete disappearance of P vacancy related deep level upon hydrogenation. In this paper we report the effects of sulfide treatment of p-InP on the Schottky barrier height and room temperature PL. The surface and bulk "passivation' effects by hydrogenation of p-InP are also presented. Mat. Res. Soc. Symp. Proc. Vol. 262. C1992 Materials Research Society
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