Deep Level Luminescence in InP: Phonon Feature Analysis
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DEEP LEVEL LUMINESCENCE IN InP: PHONON FEATURE ANALYSIS S.BANERJEE, A.K.SRIVASTAVA, AND B.M.ARORA Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400005, India
ABSTRACT The phonon features in the deep level luminescence (PL) bands related to Fe and Mn and native defects in InP have been clearly identified and the lineshape of the bands are analysed using configuration coordinate model. A consistent set of phonon parameters are determined for the first time.
INTRODUCTION Presence of impurities and native defects in semiconductors are mainly responsible for the deep levels in the band gap region affecting the electrical and optical properties. Photoluminescence (PL) spectroscopy has been widely used to identify defects that modify the optical properties of the material. In undoped InP the deep level PL is characterized by several broad bands between 0.9 - 1.3 eV. The identification of the deep level components in undoped InP is quite difficult due to the very low intensity of the deep level PL emissions. The deep level PL in undoped InP has been associated with residual Fe and Mn [2,5], In- and P- vacancies, P-interstitial (native defects) and their complexes [2,5,6]. Distinct phonon related structures have been observed in the PL bands due to the strong interaction of the defects with the lattice. However, there is a lack of consensus on the parameters (such as zero-phonon transition energy, phonon energy and the phonon coupling strength) that describe the individual bands related to Fe and Mn and the native defects [1-5]. The main problem in obtaining a consistent set of parameters for a given defect is 1) often the phonon related features are broad and not distinct, and 2) the spectral features are modified due to many impurity bands present in the same energy range. We have observed distinct phonon related features in the PL bands related to Fe and Mn, and the band C (for the first time) in bulk grown LEC InP and analysed them using configuration coordinate model. We have obtained a set of sample independent parameters which can describe the deep level PL features in many samples consistently.
EXPERIMENTAL TECHNIQUES Bulk grown LEC InP doped with Fe and Mn, and undoped InP before and after heat treatment (in an open tube set-up at 500-5500C with flowing 112) are used in this study. The samples mounted in a closed cycle He refrigerator are excited by 488nm line of Ar ion laser. The luminescence from the samples (at 10K) is analysed by a 0.67m grating monochromator and detected using a liquid nitrogen cooled Ge detector together with a lock-in amplifier.
RESULTS AND DISCUSSION Deep level PL spectra of InP doped with Fe and Mn are shown in Fig.1 and Fig.2, respectively. The Fe band in Fig.1 is centered near 1.08 eV and has a full width at half maximum (FWHM) of about 0.15 eV. The spectrum clearly shows the phonon features (indicated by arrows in Fig.1). In F19.2 the the main feature ig a broad band with peak at nearly 1.15 0.1and 1'IIM of 0.12eV. A shoulder is also seen on the high energy side o
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