OMVPE of InAlAs Using Alternative Al and As Precursors
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OMVPE of InAlAs Using Alternative Al and As Precursors Brittany L. Smith1, Nichole M. Hoven1, Glen Hillier2, Seth M. Hubbard1, David V. Forbes1 1
Rochester Institute of Technology, 25 Lomb Memorial Drive, Rochester, NY 14623, U.S.A.
2
MicroLink Devices, 6457 W Howard St, Niles, IL 60714, U.S.A.
ABSTRACT Alternate aluminum and arsenic precursors were investigated for InAlAs grown by organometallic vapor phase epitaxy (OMVPE). The quality of the InAlAs growths was investigated by secondary-ion mass spectrometry (SIMS) to measure impurity concentrations. Trends are extracted from SIMS measurements for each precursor as a function of V/III ratio and growth temperature. Two arsenic precursors, arsine and tertiarybutylarsine (TBAs), were chosen to compare InAlAs growth quality. The impurity concentrations measured by SIMS decrease as the V/III ratio increases, for both arsine and TBAs growths. Impurities also decrease as growth temperature increases. Two aluminum precursors, trimethylaluminum (TMAl) and tritertiarybutylaluminum (TTBAl), were used to compare the effect of alumimum precursor on carbon and oxygen impurity levels. TMAl is widely studied in literature, though TTBAl is less common. This study represents the first report using the TTBAl precursor for InAlAs growth. Each aluminum source is used in conjunction with each aforementioned arsenic precursor in order to compare all possible precursor combinations. TMAl growths demonstrated decreasing impurities with increasing V/III ratio. TTBAl growths did not exhibit such a dependence, impurity concentrations remained virtually constant regardless of V/III ratio. INTRODUCTION The ternary alloy InAlAs lattice-matched to InP is an attractive candidate for a variety of devices, including high electron mobility transistors, high-performance heterojunction bipolar transistors, and other opto-electronic devices [1, 2]. High quality materials are necessary for such applications, and OMVPE has been reported to yield smaller defect densities than molecular beam epitaxy which can sometimes produce resistive epilayers [2]. Certain OMVPE growth parameters can be altered in order to produce the highest quality material. These parameters include the chemical composition of the organometallic precursors, the molar flow ratio of Group V elements to Group III elements (known as the V/III ratio), the growth temperature, and the growth rate. The growth of aluminum containing materials such as AlGaAs and InAlAs by OMVPE often suffers from unintentional incorporation of impurities such as carbon and oxygen. Carbon is inherent to the OMVPE process as the metalorganic sources contain methyl- or ethyl- organic ligands. Oxygen is a particular problem for aluminum containing materials due to the high Al-O bond strength. Minimizing the C, and O impurity background using optimized epitaxial growth conditions is well-documented for AlGaAs [10-12] with the growth temperature and V/III ratio among the strongest process variables that control the carbon and oxygen impurity levels.
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