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HL: Halbleiterphysik

HL 23: GaN I

HL 23.3: Talk

Tuesday, March 27, 2001, 16:00–16:15, S2

Flow modulation growth of GaN by hydride vapor phase epitaxy — •Wei Zhang¹, Helder R. Alves¹, Dirk Meister¹, Detlev M. Hofmann¹, Bruno K. Meyer¹, Till Riemann², Peter Veit², Alois Krost², and Juergen Christen² — ¹I. Physics Institute, Justus-Liebig-University Giessen — ²Institute of Experimental Physics, Otto-von-Guericke- University Magdeburg

Conventional growth of GaN films on Al₂O₃ substrates tends to result in high threading dislocation densities (10⁸ - 10¹⁰ cm⁻²) and unsatisfactory morphology of the films due to the large lattice mismatch between GaN and the substrate. Techniques using buffer layers, pretreatments of the substrate and epitaxial lateral overgrowth have recently been applied to improve the crystaline quality of GaN. In this work we demonstrate the effect of flow modulation on the growth of thick GaN by hydride vapor phase epitaxy (HVPE) to reduce the dislocation density and to improve layer morphology. The flow modulation growth was carried out in a custom vertical HVPE system. The reactive species were injected periodically into the reactor to realize the modulation of the flow. Optical microscopy shows that the GaN films are very smooth, almost crack-free. Cathodoluminescence and transmission electron microscopy of the cross-sectional structure exhibit that there is a seperated multilayer structure in the GaN films. The dislocation density decreases from 10¹⁰ cm⁻² in the initial layer to 10⁷ cm⁻² in the top layer. This shows that flow modulation growth is a useful technique to improve the cystaline quality of thick GaN films.