Oxygen-Related Defects in In 0.5 (Al x Ga 1-x ) 0.5 P Grown by MOVPE
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ABSTRACT Oxygen related defects in Al-containing semiconductors have been determined to degrade luminescence efficiency and reduce free carrier lifetime, affecting the performance of light emitting diodes and laser diodes. We have used the oxygen doping source, diethylaluminum ethoxide, (C2H5)2A1OC 2H5 , to intentionally incorporate oxygen-related defects during growth of Ino. 5(AlxGa 1 -x)0.5P by Metalorganic Vapor Phase Epitaxy (MOVPE). Our investigations have identified several defects which are 'intrinsic' or present in non-intentionally oxygen-doped n-type In0. 5(AlxGa1 x)0.5P as well as those due to oxygen, which introduces defect states near the middle of the conduction band. Deep level transient spectroscopy and photoluminescence data obtained for these defects over a range of composition, are presented illustrating the trends in defect structure with alloy composition. The impact of oxygen contamination on the visible emission spectrum is presented and discussed in terms of the defect structure.
INTRODUCTION Ternary and quaternary alloys have become increasingly important in the fabrication of electronic and optoelectronic devices. The In0. 5(AlxGal-)o0. 5P alloy system, which is lattice matched to GaAs, is becoming more important in a broad spectrum of applications. This material has been used to fabricate laser diodes [l] and light emitting diodes [2] emitting in the visible spectral region. A10.51n 05.P is also used to reduce hole leakage currents in heterojunction bipolar transistors (HBT) owing to its large valance band offset to GaAs [3]. Unfortunately, some of the problems which exist within the AlxGal-xAs system are present in In o0 5(Al.Gaix)0.5 P. It is well established that oxygen is an unintentional impurity in AlxGai_xAs grown by any epitaxy technique [4]. In MOVPE growth of Al containing alloys, oxygen is incorporated at the growth front by forming a strong covalent bond with Al. Oxygen introduces non-radiative recombination pathways and reduces free carrier lifetimes, thereby reducing luminescence intensity. It also forms deep states in the band gap that can trap electrons and holes [5]. We have utilized the molecular dopant source diethylaluminum ethoxide (C2H5 OAI(C2 H5 )2 or DEA1O) to incorporate oxygen-related defects into In0.5(AlxGa1 .x)0. 5P. DEA1O incorporates oxygen in the form of an A1-O complex, providing a controlled technique for incorporating oxygen into the growing crystal. DEAIO has been used previously to effectively introduce oxygen into other binary and ternary compound semiconductors [6,7,8]. 611
Mat. Res. Soc. Symp. Proc. Vol. 484 0 1998 Materials Research Society
This study utilized a combination of Deep Level Transient Spectroscopy (DLTS), capacitance voltage (C-V), and secondary ion mass spectroscopy (SIMS) measurements to determine the concentration and electronic structure of defects both nominally present in these materials and introduced by oxygen in InO.5(AlxGalX)0. 5P.
EXPERIMENT Ino.5(AlxGai-x)o.sP layers, 1 -tm thick, were grown on GaAs substrates. The bac
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