Ambipolar carrier diffusion in In0.53Ga0.47As single quantum wells

Abstract

The microluminescence surface scan technique MSST has been used to investigate photocarrier di usion in undoped In0:53Ga0:47As -InP single quantum well QW , in the temperature T range from 15 K to 295 K. Narrowing of the photoluminescence PL spatial pro le is observed as the temperature is lowered, indicating reduction of the photocarrier di usion length upon cooling. It was found that the width of the PL spatial pro le follows a linear function of temperature, but a change in slope by a factor of 2.6 is observed at about 200 K, indicating a change of the dominant carrier scattering mechanism. In the temperature range of 15 K to 200 K, the ambipolar photocarrier di usion mechanism seems to be correlated to impurity states thermally activated. I IntroductionInvestigations of photocarrier transport properties in two-dimensional heterostructures have a great deal of interest, since they play a central role in the design and operation of photovoltaic devices. Experimental techniques which incorporate spatial resolution capabilities have been recently developed, being used to investigate the physical processes of light emission and photocarrier dynamics in semiconductor quantum wells QW . Cathodoluminescence CL 1 and optical beam induced current OBIC 2 have been extensively used to measure the carrier di usion length. An early study of photocarrier transport used a spatially scanned pumpprobe technique for imaging the in-plane motion 3 . The microluminescence surface scan technique MSST has been recently applied to study the photocarrier transport mechanism in bulk semiconductors 4 . In the MSST, a tightly focused laser beam is used to excite the sample surface, and the lateral spread of electron-hole pair is observed by scanning the microluminescence image at the focal plane of the system. Such a measurement allows the determination of the e ective di usion length of the photoexcited carriers, which in turn provides indirect information about parameters as important as the photocarrier lifetime and the photocarrier mobility. In this work, we use the MSST setup to investigate the transport properties of photocarriers in an undoped single QW of InGaAs lattice-matched to InP, in the temperature range of 15 K to 295 K. II ExperimentThe lattice-matched InGaAs-InP single QW LV 614 used in this study was grown by V apor Levitation Epitaxy VLE 5 . The nominally undoped sample consists of a 0.6 m InP bu er layer epitaxially grown on top of an InP substrate, followed by a 110 A thick InGaAs layer, and covered with a 600 A InP cap-layer. The sample was mounted in a temperature-controlled optical cryostat, and optically excited using an Ar + -ion laser tuned at 514 nm, which provides energy excitation above the InP band gap. The laser beam was focused dow n t o a s p o t o f 4 m in diameter, thus allowing lateral photoluminescence PL measurements with very good resolution. The radial PL intensity distribution is chopped, synchronously ampli ed and measured using a Nitrogen-cooled Germanium detector, as described elsewhere 6 . P...