Low Temperature Growth of Gaas Quantum Well Lasers by Modulated Beam Epitaxy
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LOW TEMPERATURE GROWTH OF GaAs QUANTUM WELL LASERS BY MODULATED BEAM EPITAXY S. XIN, K.F. LONGENBACH, C. SCHWARTZ, Y. JIANG AND W.I. WANG Department of Electrical Engineering Columbia University, New York, NY 10027 ABSTRACT GaAs single quantum well lasers have been successfully grown at low temperatures by a modulated beam epitaxy process in which the Al/Ga flux is held constant while the As flux is periodically shut off to produce a metal-rich surface. Devices grown at a substrate temperature of 500 °C exhibit threshold current densities below 1 kA/cm 2 . This value is lower than normally grown low temperature lasers and is the lowest achieved by any low substrate temperature growth technique. In addition, low temperature (10 K) photoluminescence of single quantum wells grown with this technique exhibit full-width half maximum values, comparable to that attainable by higher temperature growth techniques. The improved quality of these low temperature grown quantum structures is attributed to both a smoothing of the growth front and a reduction of excess As during the modulated beam epitaxy process. The high growth rates and less frequent shutter operation of this technique make it a more practical than migration enhanced epitaxy or atomic layer epitaxy for low temperature growth. Introduction The low temperature growth of laser diodes is motivated by the desire to integrate optical devices with completed electronic devices for opto-electronic applications. It is well established that molecular beam epitaxial(MBE) growth at high temperatures produces significantly lower threshold current densities than low temperature growth[I-3]. However, at these high temperatures it is very difficult to maintain sharp doping profiles and abrupt heterointerfaces. As a result, migration enhanced epitaxy (MEE) has been employed to grow III-V quantum well structures at low substrate temperaturess[4,51. In this technique, growth is controlled by alternately opening and closing the shutters of the Group III and Group V elements every few seconds. Although this enhances the material quality of low temperature grown materials, this technique is not practical for the growth of thick structures like quantum well lasers since the growth rate is too slow and the shutters operated too frequently. Furthermore, Mat. Res. Soc. Symp. Proc. Vol. 228. @1992 Materials Research Society
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both the slow growth rates and growth interruption in MEE techniques enhance impurity incorporation which may be undesirable[6,7] for device applications. In this paper we report the growth of high quality single GaAs/AlxGaj-xAs (x=0.35) quantum well structures grown at 500 °C by a modulated beam epitaxy process. In modulated beam epitaxy, the As shutter is periodically opened and closed while the Ga and/or Al furnace is held constantly open. With this procedure high growth rates are maintained and high quality heterostructures can be produced at substrate temperatures substantially lower than typically used for high quality molecular beam epitaxial (MBE) growth
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