GROWTH OF GASB ON GAAS SUBSTRATES

The initial growth of GaSb on GaAs substrates by atmospheric pressure metalorganic vapour phase epitaxy (MOVPE) has been investigated both in-situ and ex-situ. The in-situ technique used was quasi-elastic light scattering (QLS) and the ex-situ technique was atomic force microscopy (AFM) measurements. Both techniques show that there is a narrow range of III:V ratios where good island nucleation can be achieved. Both techniques also show that the islands grow anisotropically along the [110] directions. At low growth temperatures (less than or similar to 520 degrees C) they are longer along the [110] direction; at similar to 540 degrees C they are nearly square, and at high growth temperatures (greater than or similar to 560 degrees C) they are longer along the [($) over bar 110] direction. The size, shape and number density of the islands depend on the III:V ratio, growth time, growth rate and growth temperature. At low growth temperatures and growth rates it has not been possible to observe full coalescence of small islands using the usual trimethyl alkyls, so triethylgallium (TEGa) and tertiarybutlydimethylantimony (tBDMSb) have been used instead. These have much better pyrolysis characteristics (25% pyrolysed at 520 degrees C compared with 5%) and give much more efficient growth. This combination has allowed full coalescence of small islands grown at 520 degrees C for the first time. The improvements achieved in the morphology of thick layers of GaSb on GaAs have allowed us to fabricate a novel InAs/GaSb ballistic transport device.