A Novel Approach to the Assessment of Semiconductor Hetero-Interfaces in Multilayer Structures
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A NOVEL APPROACH TO THE ASSESSMENT OF SEMICONDUCTOR HETERO-INTERFACES IN MULTILAYER STRUCTURES J.S. RIMMER, M MISSOUS, A.R. PEAKER (Dept. of Electrical Engineering and Electronics) B. HAMILTON (Dept of Pure and Applied Physics) The Centre for Electronic Materials, University of Manchester Institute of Science and M60 1QD, United Kingdom.
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ABSTRACT We demonstrate the novel use of CV simulation to determine the level of charge at each interface in multilayer GaAs/AIGaAs heterostructures. The gettering of charged centres at the earliest grown interfaces is quantitatively appraised and the parallel application of PL decay lifetime measurements determines their effectiveness as recombination centres. A direct relationship is found between the magnitude of the charged states and the recombination velocity. Estimates of a I eV activation energy and a hole capture cross 2 section of 10-1s cm were also obtained. This suggests that the dominant recombination centre could be observed as a hole trap.
INTRODUCTION The existence of charged mid-gap states or recombination centres at the interfaces of semiconductor heterostructures is a problem of long standing. Estimates of the level of charge at a single interface have recently become possible by examining the apparent carrier concentration profile obtained from CV measurements [1]. The GaAs/AIGaAs interface has been investigated extensively using CV and DLTS techniques including spatial profiling of the identified deep levels but there seems to be little agreement in the measured characteristics of the traps between different reports [2,3,4]. Measurements of interface recombination velocities in double heterostructures (DH) have been used as an indication of interface quality [5,6,71 and also to determine the effect of thin prelayers on the active region interfaces [8]. These DH structures must necessarily have thin optically active regions so that interface recombination will be the dominant process [9], if prelayers are included then the resulting structures may be relatively complicated. It is therefore clear that the levels of interface charge in these multilayer structures cannot be obtained by direct examination of the CV profile as in the case of a single interface so that determining the sheet charge density presents a considerable problem. Computer simulation of CV profiles has also become established as an investigative technique. However, until recently, computer models have been restricted to a single interface and have often been beyond the capabilities of desk-top computers or required considerable run times in the case of multilayer structures. Their use has been limited to investigating the inherent limitations of conventional CV profiling [10,11,12,13] or as a check against band offset and interface charge measurement at single interfaces [14,15]. However, a new, fast CV simulator has been developed by us [16] which runs on a desk-top computer and can provide simulated profiles of multilayer structures in a matter of min
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