Diamond Heteroepitaxial Lateral Overgrowth
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Diamond Heteroepitaxial Lateral Overgrowth Y-H Tang, B. Bi, and B. Golding Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-2320, U.S.A. ABSTRACT A method of diamond heteroepitaxial lateral overgrowth is demonstrated which utilizes a photolithographic metal mask to pattern a thin (001) epitaxial diamond surface. Significant structural improvement was found, with a threading dislocation density reduced by two orders of magnitude at the top surface of a thick overgrown diamond layer. In the initial stage of overgrowth, a reduction of diamond Raman linewidth in the overgrown area was also realized. Thermally-induced stress and internal stress were determined by Raman spectroscopy of adhering and delaminated diamond films. The internal stress is found to decrease as sample thickness increases. INTRODUCTION The crystal quality of chemical vapor deposition (CVD) diamond is often affected by the presence of dislocations, leading to internal stresses. In addition, dislocations may act as electronic traps, degrading carrier mobilities. Heteroepitaxially grown diamond, with imperfectly lattice-matched substrates and buffer layers, not only possesses interfacial and threading dislocations [1], but can have an additional stress contribution due simply to thermal effects on cooling from its growth temperature. The limited selection of suitable lattice-matched substrates and buffer layers suitable for diamond growth has impeded advances in structural perfection. Epitaxial lateral overgrowth (ELO) is a means for limiting the propagation of threading dislocations into the growing material. A number of variants have been used for III-V semiconductor growth with significant success.[2-4]. However, ELO has not been widely studied in heteroepitaxial diamond growth. Ando et al.[5] first adapted the ELO concept to (001) diamond grown on (001) MgO substrates with a (001) Ir film as buffer layer in DC-plasma CVD. Their method is based on the necessity to expose the Ir surface to hydrocarbon ion bombardment prior to growth to prepare the Ir surface, referred to as “bias-enhanced nucleation” or BEN. The BEN surface is first patterned by electron-beam lithography, followed by an ion beam bombardment that inhibits diamond formation in exposed areas. CVD diamond growth is then initiated from the protected Ir regions and overgrowth proceeds onto the damaged Ir areas. Threading dislocations, generated at the Irdiamond interface, are therefore less likely to propagate into the overgrown diamond regions. Washiyama et al.[6] later applied the same ELO method to study the crystal quality of diamond at coalescence boundaries. They found that the Raman linewidth of ELO diamond above the overgrown diamond layer was reduced. In this work, we describe a novel diamond ELO method which utilizes a thermallyevaporated metal mask on a previously grown thin diamond layer. Owing to the aggressive chemical and thermal environment in a CVD reactor, only few materials are suitable as the masking layer. Gold has a number of adva
