The Anodization of GaAs and GaP in Aqueous Solutions

Abstract

The anodic oxidation of normalGaAs and normalGaP in properly conductivity‐ and/orpH‐adjusted water has been successfully demonstrated under both constant voltage and constant current conditions. With H3PO4 as the acidic conductivity/pH modifier, uniform, well‐controlled oxides have been grown in thepH range 2.5–3.5. The oxide thickness‐voltage relationships for both normalGaAs and normalGaP are linear, with slopes of approximately 20 and 12 Å/V, respectively. At room temperature, oxides as thick as 3600 and 2000Å can reproducibly be grown on normalGaAs and normalGaP , respectively; at 100°C, an oxide as thick as 5000Å has been grown on normalGaAs . Under basic conditions, with NH4OH as the conductivity/pH modifier, oxides have been grown in the pH range of 10–11, but dissolution of the oxide in the bath results in much poorer control than in the acidic system; this dissolution effect can be utilized more in the line of electroetching than in simple oxide formation. Anodic oxidation, with relatively little oxide dissolution, has also been accomplished in near neutral‐pH water (i.e., ∼7) with false(NH4)2HPO4 as the conductivity/pH modifier. Restricted‐area oxidation and/or etching has been demonstrated whereby a prefabricated photoresist pattern is used to define restricted areas for anodization; lines as narrow as 5μ wide are readily delineated. Anodization in aqueous solutions containing either Cl− or NO3− ions is shown to result in simple electroetching, and current densities in the range 10–20 mA/cm2 are demonstrated to be most effective for controlled electroetching. The grown oxides are soluble, in normalHCl , HNO3 , and H2SO4 , and are affected by prolonged contact with water. If properly baked, however, the oxide grown on normalGaAs shows no evidence of change in months of storage in laboratory air; the oxide grown on GaP does show evidence of moisture absorption after 1 month of equivalent storage. A preliminary analysis of some of the controlling electrical factors during anodization shows that under constant voltage conditions, the current false(Ifalse) varies asI=ABt+Cand under constant current conditions, the time derivative of the voltage is a constant.

Photovoltage effects in photoemission from thin GaAs layers

“…Since heavy p-type doping is necessary to achieve a NEA surface, a 0. In order to preserve an atomically clean surface the samples were anodized to form an oxide layer of about 50Å on the GaAs surface 22 . The oxide layer was later removed as described below.…”

Cation and Anion Transport Numbers in Anodic GaAs Oxides

“…Not surprisingly the oxide of GaAs has also received considerable attention. Many studies have characterized the oxidation kinetics in a variety of electrolytes (1)(2)(3) and have measured the oxide composition profile (4)(5)(6). The electrical properties of the oxide and the oxide-semiconductor interface have also been reported in the literature (3,5,7,8).…”

A very high charge, high polarization gradient-doped strained GaAs photocathode

“…On top of the active layer, the GaAs surface layer with thickness from 10 to 45 nm was grown with a doping concentration of 5×10 19 cm −3 . In order to preserve an atomically clean surface the samples were anodized to form an oxide layer on the GaAs surface [11]. The oxide layer was later removed as described below.…”

“…An anodization/stripping technique was then used to prepare samples of different surface layer thickness for polarization and QE measurements. The anodization/stripping technique consisted of a self-terminating anodization at a given voltage forming an oxide layer [11] and a stripping of the resulting oxide layer in an ammonium hydroxide solution followed by rinsing in distilled water and methanol. Using this technique, the GaAs surface layer can be removed at the rate of 1.5 nm/V as described in the next section.…”