Electrochemical Measurements of Interface States at the GaAs / Oxide Interface

Abstract

Electrochemical measurements are used to measure the interface state density at the GaAs/oxide interface. The techniques are described, including, for example, the use of dimethyl formamide as the solvent to avoid etching the oxide. The advantages of the "EOS" meaasurement over the standard MOS measurement are outlined and demonstrated. Several advantages are realized, stemming primarily from the fact that the inert electrolyte blocks the current flow. With the MOS technique, a conducting oxide can make the interpretation very difficult. Preliminary measurements on clean and anodically oxidized n-and p-type GaAs are presented. The interface state density is shown to be sensitive to anodization current programming and to low temperature annealing of the oxides.The measurement of the interface state density under a passivating oxide layer is important in the production of semiconductor devices. The ability to produce MOS devices depends on a low interface state density, and the development of techniques for preparing passivating layers of low interface state density depends on the ability to measure this density. Electrical techniques to measure energy on interface state levels are also valuable for understanding the chemistry of native oxide growth. For example, the SiO~/Si system is now one of the best understood oxides, primarily because of the excellent electrical methods (1) that have been developed for its study. The standard method used to study the Si/SiO~ interface involves the MOS (metal-oxide-semiconductor) configuration, where a relatively high potential applied to the metal layer induces charge at the semiconductor surface. Part of the induced charge appears in the interface states and causes a Fermi energy shift. By one of several analyses (1) based on capacity measurements, highly sensitive determinations of interface state densities down to 1010 cm -~ are possible.Measurement of interface state density at the oxidized GaAs surface has proved much more difficult (2) than the corresponding measurements at the Si/SiO~ interface. For example, high oxide leakage currents and bulk carrier trapping lead to measurement problems.An EOS (electrolyte-oxide-semiconductor) technique should have advantages that overcome many of the difficulties and permit interface state density measurement on GaAs. The two major advantages at our disposal are the use of an inert (indifferent) electrolyte and the ability to easily measure the oxide-free surface. The problem of the oxide leakage current can be prevented with the indifferent electrolyte because in this case there is an extremely low density of accessible states in the solution which can participate in electron exchange with the solid. The lack of electron exchange with the electrolyte also avoids another difficulty--the equilibrium of the interface states with the wrong Fermi energy. In fact, measurements are presented below where active ions are intentionally introduced to show that when current is allowed to flow freely across the oxide, the interface state charg...

Charge transport at the interface of n-GaAs (100) with an aqueous HCl solution: Electrochemical impedance spectroscopy study

“…In accordance with the obtained imped ance spectra, the capacitance of the surface states at U OCP applied to the semiconductor is about 0.25 and 0.45 μF/cm 2 in the dark and under daylight condi tions, respectively. The corresponding density of occu pied surface states, N SS , can be roughly estimated from the values of the capacitance as N SS (ε F ) ≈ C SS /e, where e is the elementary charge [17]. In accordance with this formula, the densities of occupied surface states in the dark and under daylight conditions are 1.6 and 2.8 × 10 12 cm -2 eV -1 , respectively.…”

Surface Charging Effects during Photoanodic Dissolution of n ‐ GaAs Electrodes

“…[1] and [2]. In order to get an estimate of the various capacitances, we assumed that the oxide thickness is directly proportional to the potential drop across the oxide (15). Using a proportionality constant for the potential dependence of the film thickness in the range 1.5-4.0 nm/V, as expected for anodic films on GaAs (15), we showed that Css >> Csc.…”

“…Co~(V --VFB --Vsc) = Qsc "~-Qif [6] The potential drop across the depletion layer Vsc can be calculated from the measured value of Csc (see Table I) via the Mott-Schottky relation (15) (e.oNDe ~'/" Vsc--…”

Electrochemical and Photoelectrochemical Behavior and Selective Etching of III–V Semiconductors in H 2 O 2 as Redox System

“…It is well known that a high concentration of surface and interface states is always present at the surface of GaAs, especially near the middle of the bandgap (27,28) and if the surface is oxygen covered (29,30) as after etching by acidic H202 mixture (31). According to experiments conducted in vacuo, these electronic states often result from dangling bonds or a different band structure of surface atoms which have a high reactivity for the solvent (32).…”