Thermal Oxidation of III-V Materials and Heterostructures

Abstract

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...

Composition and growth of anodic and thermal oxides on InP and GaAs

“…7 Regarding thermal films on InP, AES depth profiles show that films formed in oxygen or moist nitrogen are mainly In 2 O 3 with some phosphorus throughout the entire oxide layer. 8 The phosphorus level varies from ¾5 to 10 at.% depending on the oxidation conditions; it appears to fall with increasing temperature (from 300 to 500°C) and increasing oxidation time. Similar O 1s XPS spectra to the anodic oxide shown in Fig.…”

Modern Analytical Techniques in High Temperature Oxidation and Corrosion

“…In InP-based heterostructures, InAlAs is usually sandwiched between InGaAs layers on InP substrates. It was found previously [24] that InAlAs could be preferentially oxidized in these structures, much like AlGaAs described above. A factor of 80:1 can be achieved in moist nitrogen.…”

“…AlGaAs and GaAs/AlGaAs Heterostructures. Oxides formed on AlGaAs in oxygen at 500°C comprise mainly Al and Ga and, as found for GaAs, As enrichments occur at both the gas/oxide and oxide/substrate interfaces [24]. Oxidation in moist nitrogen results in significantly enhanced oxidation compared with GaAs.…”

“…This section considers the oxidation of GaAs and Al-containing III-V materials. Al-containing oxides on AlGaAs and InAlAs [10][11][12][13] and InAlP [14][15][16][17] have been found to possess good insulating properties which make the films potentially useful for some device applications.…”

“…The lateral penetration of oxide formed at 500°C in moist nitrogen in AlGaAs layers sandwiched between 100-nm layers of GaAs depends on the thickness of the AlGaAs layer. The oxide penetration is found to increase with layer thickness until it levels off at a thickness of ~300 nm or so [13]. The average oxide penetrations in moist nitrogen are included in Table 1.…”