A Critical Comparison Between Movpe and MBE Growth of III-V Nitride Semiconductor Materials for Opto-Electronic Device A
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parallel shorting for vertical device structures. These findings support the widespread acceptance of MOVPE, rather than MBE, as the epitaxial growth technique of choice for III-V nitride materials used in vertical transport bipolar devices for optoelectronic applications. INTRODUCTION The recent development of III-V Nitride semiconductor devices for optoelectronic applications has been driven by improvements in the epitaxial growth of these semiconductor materials. Heterostructures have been fabricated across a range of AIN-GaN-InN compositions with bandgaps ranging from 6.2 eV (ultraviolet) to 1.9 eV (red) for LED, laser diode, and photodetector applications [1,2]. Heterostructure epitaxy has traditionally been performed using either MBE or MOVPE in many semiconductor material systems [3,4]; however, most of the recent device application demonstrations for III-V nitrides have used MOVPE, particularly in the commercially driven work at Nichia Chemical and Cree Research [5,6]. MBE growth for optoelectronic device applications has lagged behind. Initially, this was attributed to the unavailability of an appropriate source of active nitrogen species for MBE [1]. Through the development of nitrogen rf plasma sources for MBE, the quality of the resulting epitaxial layers has improved [7,8,9,10]. Despite these advances, demonstration of high quality vertical devices such as laser diodes or high brightness LEDs grown by MBE has not occurred [8,11 ]. In this work, we compare the growth of III-V nitride materials by MBE and MOVPE in order to examine the fundamental differences in the epitaxial growth and the influence on G 5.10 Mat. Res. Soc. Proc. Vol. 537 © 1999 Materials Research Society
resulting devices. We have studied three areas of critical importance for light emitting devices. First is the difference in the epilayer growth morphology; second is the doping of GaN with magnesium for p-type conductivity; and finally, the deposition of InGaN quantum wells with compositions in the visible emission range. This comparison provides a twofold benefit of identifying critical areas for further exploration in crystal growth and deepening the understanding of the underlying physical processes at work in successful epitaxial deposition. EXPERIMENTAL PROCEDURE MOVPE growth was performed in a vertical flow rotating wafer (up to 2000 rpm) system designed and built at NCSU. A radiatively heated substrate mount, of original high reliability design, can achieve temperatures up to 1200°C, as measured by an optical pyrometer.
50-mm
diameter sapphire wafers were used as the base substrate with a typical low temperature GaN nucleation layer. Trimethylgallium (TMGa), trimethylaluminum (TMAI), trimethylindium (TMI) and ammonia were used as precursors with nitrogen and hydrogen carrier gases at a reactor pressure of 76 Torr. Silane and bis(cyclopentadienyl) magnesium were used as dopant sources. Growth temperatures for GaN ranged from 1060°C to 1130°C. The conditions resulted in 2D epitaxial growth at rates of 1-2 itm/hr. InGaN growth
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