ELSEVlER zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA applii Applied Surface Science 117/l 18 (1997) 776-780 surface science Characterization of InP S-doped with Er by FFT photoreflectance Jiti Nukeaw *, Naoteru Matsubara, Yasufumi Fujiwara, Yoshikazu Takeda zyxwvutsrqpon Department of Materials Science and Engineering, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku. Nagoya 464-01, Japan Abstract InP S-doped with erbium (Er) by organometallic vapour phase epitaxy (OMVPE) has been systematically investigated by room-temperature photoreflectance (PR) spectroscopy. The PR spectra are observed with many periods of Franz-Keldysh oscillation (FKO) above the band-gap energy due to an electric field existing in the epitaxial layer. Fast Fourier transform (FFT) is successfully applied to the PR spectra to calculate the electric field precisely from the FKO. The transformed spectra exhibit two peaks clearly. The main peak corresponds to the FKO, while the other peak to the split-off transition. The electric field deduced from FKO decreases with the increasing cap-layer thickness and the Er-exposure duration. Behaviours of the electric fields are discussed based on the existence of ErP. Keywords: Photoreflectance; Erbium; &doping; InP; Electric field 1. Introduction electric field between the &doped layer and the surface [6]. Rare-earth (RE) doped III-V semiconductors have Based on FKOs observed in the PR spectra, the been intensively investigated due to their possible electric field and, hence, the Fermi level can be application to optoelectronic devices. Er is of partic- accurately determined. Information about the charge ular interest because the intra4f shell transitions transfer mechanism at the surface and the interface from the first excited state (4I13,2) to ground state can also be obtained since PR is an optical response (41,s,2) of the Er3 + ions result in sharp lumines- of the system to the modulating field. cence lines near 1.54 pm, which is in the range of minimum transmission loss of silica-based optical fibers [l-4]. In this paper, we report the PR results in a series of InP samples &doped with Er by organometallic vapor phase epitaxy (OMVPE). Photoreflectance (PR) is a powerful technique for investigation of electronic properties of semiconduc- tor heterostructures [5]. PR spectra of &doped struc- tures have been described as the main PR feature and Franz-Keldysh oscillation (FKO) arising from an 2. Experiments The Er &doped grown on Fe-doped structures in this study were semi-insulating InP substrates * Corresponding author. Tel.: + 81-52-7893620; fax: + 81-52- 7893239. with a surface orientation of (100) by OMVPE [7]. In the OMVPE growth of InP, trimethylindium (TMIn) and tertiarybutylphosphine (TBP) were used as source 0169-4332/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved. PZZ SO 169- 4332(97)00153- O