Some Observations Concerning GaAs Anodic Oxides

Abstract

The efficiency of anodic oxide formation, Cox, on nGaAs in an electrolyte formulated by Hasegawa and Hartnagel (1) depends on the applied current density (2). In contrast, there is no evidence of parasitic reactions associated with the semiconductor-oxide interfacial charge transfer (2, 3), hence the faradaic efficiency, Cf = 1. The less than 100% efficiency of the growth process may be attributed to: (i) transport of reaction product(s) to bulk electrolyte prior to completion of surface coverage (1, 2), (ii) dissolution of oxide layer on contact with an electrolyte (1, 2) and (iii) transport of nonparticipating species across the growing oxide layer into the bulk electrolyte (2).This preliminary note is concerned with the effect of growth rate on the accumulation of diffusing substances in the omde layer and on the oxide structure. ExperimentalAnodic oxides were grown galvanostatically, employing standard procedures and apparatus. Potential decays on open circuit, following current interruption, were c~ispiayed on a tfewlett-Packard, Model 7001 AM X-Y recorder. Oxide layers were examined with a I-litachi HU-125 electron microscope operated at 125 kV. Specimens for the microscopic examination were prepared by ion milling from the GaAs substrate side until a small hole was observed. Areas around the hole were sutliciently thin to yield good images. Results and DiscussionE~ectrode behavior on approach to Vres~.--An approach to the electrode rest potential upon the termination of oxide layer growth to a predetermined thickness, as a function of growth rate, is illustrated in Fig. 1. Qualitatively, the difference in the electrode transient behavior between the fast (solid lines) and the slow (dashed lines) growth rates increases with an increase in the oxide layer thickness. The slow approach to Vrest and its dependence on the oxide layer thickness rules out the participation of potential affecting processes within both the electric double layer and the depletion and/or space charge layer. Consequently, the processes responsible for the observed behavior ought to be confined to the oxide layer.It was shown (2) that anodic oxidation of n-GaAs obeys a relationship j = A exp(~E/RT) [1] The empirical constant A is related to molecular diffu-* Electrochemical Society Active Member.

GaAs Oxidation and the Ga‐As‐O Equilibrium Phase Diagram

“…Anodic and plasma oxidation.--The situation for electrochemically (9-10, 15-23) and plasma (24-28) oxi-dized GaAs (Table V) stands in distinct contrast to what was observed for the case of thermal oxidation. Room temperature electrochemical anodization leaves amorphous oxide films (15,16) whose major phase constituents are Ga20~ and As20~ (9,10,24). Water and As2Q have been observed to volatilize from films anodized in aqueous base electrolytes during heating (20).…”

Some Aspects on the Mechanism of Anodic Oxidation of GaAs

“…Actually it is obviously shown that the greater the ratio of glycol in AGW electrolyte, the smaller the critical current density is Jc (1: 1) --0.15 mA/cm 2 3e (1:2) = 0.07 mA/cm s Jc (h6) = 0.02 mA/cm~ Thus we can control the critical current density by changing the temperature and composition of electrolyte. It is important that an oxide film can be grown in the AGW electrolytes at current densities less than the critical current density at room temperature, thus affecting the structure of the growing film (6).…”

Surface Roughness Studies of Native Oxides of GaAs

“…A significant amount of work has already been done in developing the various techniques to grow these oxides on GaAs surfaces (1)(2)(3). Their optical and electrical properties have been determined and the interface of the GaAs/oxide region well characterized by various surface probe techniques (4)(5)(6)(7).…”