The single-source precursor concept. A case study of gallium arsenide

Abstract

The viability of the GaAs single-source chemical beam epitaxy (CBE) precursors [Me 2Ga(μ-As i Pr 2)] 3 ( 1), [Me 2Ga(μ-As t Bu 2)] 2 ( 2), [Et 2Ga(μ-As t Bu 2)] 2 ( 3) and Ga(As t Bu 2) 3 ( 4) has been explored. Precursor 1 (and analogous trimeric molecules) fail to yield satisfactory thin films of GaAs because of facile loss of tetraalkyldiarsine. Both 2 and 3 afford epitaxial p-type films of GaAs at > 500°C and 10 −5 Torr pressure. However, thin films grown from 3 exhibit anomalous Hall mobilities due to Ga island formation. The best thin films of GaAs were grown from the homoleptic precursor 4 at 480°C and 10 −5 Torr pressure. These thin films are n-type, of low carbon content, and exhibit an exciton peak in the 4.2 K photoluminescence spectra. Pyrolysis studies (10 −2 Torr pressure) have been carried out on 1–3. These studies confirm that the diarsine As 2( i Pr) 4 is readily eliminated from 1. For both 2 and 3, the t Bu ligands begin to react at ∼330°C with formation of both isobutane and isobutene. Methane elimination from 2 commences at 445°C. However, the Et groups of 3 begin to react at a significantly lower temperature (350°C), thus explaining the formation of Ga islands. Temperature programmed desorption (TPD) studies at 2 × 10 −10 Torr pressure yield similar results and, in addition, indicate that in the case of 4 the sequence of reactions is t Bu ligand desorption, β-hydride elimination from t Bu 2As moieties, followed by H 2 desorption and Ga—As bond cleavage. The potential use of single-source precursors for nanosize particle formation, access to metastable or unusual phases, selective deposition, and growth modification is also discussed.