Surface Reaction Mechanisms Governing the Selective Area Growth of III-V Compound Semiconductors by Chemical Beam Epitax
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SURFACE REACTION MECHANISMS GOVERNING THE SELECTIVE AREA GROWTH OF III-V COMPOUND SEMICONDUCTORS BY CHEMICAL BEAM EPITAXY G J Davies*, P J Skevington*, C L Levoguer**, C L French** and J S Foord** BT Laboratories, Martlesham Heath, Ipswich, IP5 7RE, UK. University of Oxford, Physical Chemistry Laboratory, South Parks Rd, Oxford, OXI 3QZ, UK. * **
ABSTRACT Previous studies have helped elucidate the underlying mechanisms for selective area epitaxy in chemical beam epitaxy by investigating the reactions of triethylgallium (TEG) on a silicon nitride surface. However no explanation was produced as to why selective growth is lost at low temperatures or high Gp V beam fluxes. This question is addressed in this paper which examines the interaction between TEG and As2 on the silicon nitride surface. In the absence of arsenic, TEG adsorbs with a low sticking probability on the dielectric. Adsorbed species mainly desorb rather than decompose, and any Ga produced on the surface becomes converted to a nitride form; no free Ga is produced hence GaAs growth cannot occur. Arsenic is found to form a weakly adsorbed phase on the nitride surface. Reaction with co-adsorbed TEG results in the formation of GaAs. Adsorbed As also is efficient in increasing the reactive sticking probability of TEG. The results provide further insight into the reaction mechanisms governing selected area epitaxy.
1 Introduction Selected area epitaxy has emerged as an important technique for the integration of electronic and photonic devices on single crystal substrates [1]. The technique utilises semiconductor wafers on which a patterned dielectric layer is deposited. Selective area growth of GaAs [2,3],
InP [4] and InGaAs [5] have been reported using Si0 2 or Si3 N4 as the masking layer, under optimised growth conditions, no deposition is seen on the dielectric mask whilst epitaxial growth occurs on the exposed substrate through openings in the mask. Although techniques such as Metal-Organic Vapour Phase Epitaxy (MOVPE) and Molecular Beam Epitaxy (MBE) have achieved selective area epitaxy, they have significant limitations for this application. In contrast, we have demonstrated that chemical beam epitaxy (CBE) appears
ideally suited to selected area growth [6]. For example, minimised edge features are observed at the mask/semiconductor interface and the growth composition shows no mask area dependency in the case of ternary and quaternary compounds. Similarly no variations in composition or thickness of the semiconductor growth are seen as one moves away from the mask/window
interface. Recent work [7] using TEG and silicon nitride as the dielectric mask investigated the underlying causes for the selective area growth of GaAs by CBE. This was shown to be due the failure of TEG to decompose to liquid gallium on the dielectric but rather to incorporate at
defect sites in the dielectric as a gallium nitride/oxide compound. This compound formation then prevented further catalytic decomposition of the Gp III source and effectively stopped growth.
However,
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