Thermal oxide films formed on n-GaAs͑100͒ and Al x Ga 1Ϫx As (x ϭ 0.25-0.80) from 450-500°C have been characterized by Auger electron spectroscopy and electron microscopy, and the relative oxidation rates of AlGaAs in GaAs-based heterostructures and InAlAs in InP-based heterostructures have been determined. The kinetics and mechanism of oxidation depend on the particular oxidant. Selective oxidation of Al-containing layers in device structures depends on the layer thickness but is independent of the dopant level, and is optimized by oxidation in moist nitrogen ͑95°C͒. Electrical measurements have been performed on oxidized InAlAs/InGaAs heterostructure diodes.III-V materials, unlike silicon, do not form high-quality native oxides and in some ways, this has hampered the development of optoelectronic technology. The oxidation of III-V compounds, particularly of GaAs, has been studied extensively in the past, however, in efforts to try to produce successful metal-oxide-semiconductor field-effect transistors ͑MOSFETs͒ emphasis was placed on anodic oxidation. More recently, both anodic and thermal oxidation data for AlGaAs and quaternary systems have been reported 1-7 and the Alcontaining oxides have been found to possess good insulating characteristics. 3,4 The oxidation methodology can also be extended to InP-based devices where, e.g., InAlAs could serve as the oxidation layer. 8 Thus, Al 2 O 3 -containing layers offer promise as insulators in III-V technology.This paper focuses on the characterization of thermal oxides on GaAs, AlGaAs, and heterostructures for GaAs-and InP-based devices, for example, those used in vertical cavity surface emitting lasers ͑VCSELs͒ or heterojunction bipolar transistors ͑HBTs͒ which are comprised of AlGaAs sandwiched between GaAs layers or InAlAs sandwiched between InGaAs and/or InP layers. The relative oxidation rates of planar surfaces of GaAs and AlGaAs, as well as the relative lateral oxidation rates in GaAs-and InP-based heterostructures have been determined. The objective is to preferentially oxidize AlGaAs or InAlAs to produce an insulating alumina layer in device structures in an attempt to improve device performance.
ExperimentalExperiments were performed on n-GaAs͑100͒ doped with 2 ϫ 10 18 cm Ϫ3 Si, ϳ1.5 m thick layers of Al 0.8 Ga 0.2 As and GaAsbased heterostructures (GaAs/Al x Ga 1Ϫx As/GaAs, with x values of 0.25 and 0.75͒ grown by molecular beam epitaxy ͑MBE͒ on n-GaAs͑100͒, and InP-based heterostructures ͑InGaAs/InAlAs/ InGaAs/InP͒. Specimens were thermally oxidized over the temperature range 450-500°C in a variety of environments, pure oxygen and moist air ͑air bubbled through H 2 O at 25 or 95°C͒, and moist nitrogen (N 2 bubbled through H 2 O at 95°C with gas transfer through heated tubes to the oxidation furnace͒.After oxidation samples were analyzed by Auger electron spectroscopy ͑AES, PHI 650 system͒, electron microscopy, and transmission electron microscopy ͑TEM Philips EM 430T͒, operating at 250 keV and scanning electron microscopy ͑SEM, Hitachi S-4700 FESEM͒.
Re...