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OPTICAL STUDY OF THE Fe3 +-RELATED EMISSION AT 0.5 eV IN InP:Fe KLAUS PRESSEL', G. BOHNERT, A. DORNEN', AND K. THONKE'"

"4.Physikal. Inst., Univ. Stuttgart, Pfaffenwaldring 57, D-7000 Stuttgart 80 ".Abteilung Halbleiterphysik, Univ. Ulm, Postfach 4066, D-7900 Ulm ABSTRACT The 0.5 eV (2.5 gtm, 4000 cm'1) emission band in InP has been studied by optical spectroscopy. By the use of Fourier-transform-infrared photoluminescence we have been able to observe at least a three-fold fine structure in the zero-phonon transitions at 1 - 4300 cm- which are studied at different temperatures. Based on the fine structure and 6 A1 spin-flip the long decay time of 1.1 ms we ascribe the 0.5 eV emission to the ' r 3 transition of Fe 3 ÷. The excitation spectrum of this Fe +-related emission shows a characteristic fine structure at - 1.13 eV which belongs to a charge-transfer process of the type: Fe3+ + hv(1.13 eV) -- [Fe2+, bound hole]. We discuss the excitation mechanism of the 0.5 eV emission by charge-transfer states and compare the results with an 3 emission at 3057 cm"1 in GaAs, which we attribute to the same Fe ÷ transition (decay time: 1.9 ms).

Introduction and Experimental Details Indium phosphide doped with iron is the most important semi-insulating (SI) substrate material for opto-electronic devices like InGaAs lasers. In InP iron in the charge state 2+ has been observed in emission and absorption spectroscopy and iron in the charge state 3+ has been detected in electron paramagnetic resonance [1]. In this contribution we present further evidence that the 0.5 eV emission in InP is due to an 3 internal transition of Fe *. Figure 1 shows a 2.1 K Fourier-transform-infrared (FTIR) photoluminescence (PL) 1 spectrum of a SI-InP:Fe sample in the mid-infrared region. At - 2800 cm- the four characteristic Fe2 +-related emissions show up. They are due to internal 3d transitions between the 5 T"2 excited state and 5E ground state of Fe 2 +. In the region between 3600 and 4300 cm"1 another less intense Fe-related emission appears. Up to now this emission has been discussed controversely in the literature. Both Tapster et al. [2] and Leyral et al. [3] speculated that the emission might be due to an Fe related complex or to a 3 charge-transfer (CT) process of the type [Fe 2 +(ST 2), hb] 4 Fe + + hv. Leyral et al. also considered the possibility that the emission might be due to the contamination of another 3d element. Deveaud et al. obtained the long decay time of 1.5 ms in time-resolved measurements [4]. Therefore they attributed the emission to the 4T1 4-6A, transition of Fe 3 . Our additional data confirm this assignment of Deveaud et al.. In the PL experiments the samples were excited by a Ti/Sapphire laser which is tunable between 1.1 and 0.85 gim. The light was analyzed by a BOMEM DA3.01 FTIR spectrometer (res. = 0.01 cm'1). All the PL spectra were detected by an InSb detector (77 K). The FTIR-absorption spectra at about 1.13 eV were detected by an InGaAs diode. The PL excitation (PLE) spectroscopy studies were performed by the tu