Anodic Native Oxide Research Articles

D.c. dielectric breakdown in insulating films grown at low temperature on GaAs substrates

The purpose of this paper is to compare the d.c. dielectric breakdown behaviour of low temperature CVD SiO 2 films and anodic native oxides grown on n-type (n=10 18 cm −3 ) GaAs substrates

Interface width of anodic native oxide—InSb structures

Using our improved quantitative analysis of Auger electron spectroscopy (AES) depth profiles, we have found a linear relationship between the interface width of plasma- and wet-anodized InSb (111) and the oxide thickness in the range of 15–180 nm. Using a simple etching technique we have been able to ascertain that the effect was inherent to the oxidation process and not a result of the sputtering process. We have developed a theoretical model that explains the linear relationship in terms of field-enhanced diffusion and oxidation reaction. The model is based on our earlier experiments that demonstrated the oxygen diffusion through the oxide to the interface. Application of the model to the results of over 30 different AES depth profiles yields excellent agreement with the experimental observations that show that the interface width is about 0.25 of the total oxide thickness. The results support the thermodynamic model of anodization, indicating that interface formation is the last step of the oxide growth process.

Studies of SiOx anodic native oxide interfaces on InSb

We have investigated a method for passivation of InSb by vacuum deposition of SiOx on native oxide layers grown by wet anodization. We show that this multilayer dielectric approach results in improved passivation properties. Results of high resolution Auger spectroscopy reveal important information on the layer structure and composition of this passivation film. Specifically, we report the experimental observation of SiO2 formation at the SiOx anodic oxide interface. The interfacial reaction is limited to a thin layer, about 10 nm thick. The SiOx oxidation proceeds by reduction of the native oxide and formation of elemental In and Sb. The electrical features observed in the C–V curves (such as flat-band voltage, hysteresis, low-frequency-like response in the inversion region, and other deviations from the ideal curves) are explained in view of the oxidation states of In and Sb, observed at the oxide layers and at their interfaces. These correlations were used for characterization of the desired interlayer parameters.

Origin and effects of interface traps in anodic native oxides on InSb

We have investigated the wet anodization of InSb under a large variety of oxidation parameters. Results of Auger electron spectroscopy (AES) show that the oxidation produces a mixed oxide film of In2O3 and Sb2O3 containing some unoxidized Sb. 1-MHz capacitance-voltage characteristics show low-frequency-like response of the oxide-semiconductor junction in the inversion region. We have found a strong correlation between this response and the elemental Sb content in the oxide, as revealed by AES. We present a model which explains the role of the elemental Sb in terms of interface traps and charge transfer into the inversion layer. Furthermore, we describe the anodization conditions under which the combined effect is reduced and explain their role. The implications of this observation are discussed.

Observation of the trend of interface formation in anodic native oxide on InSb by marker experiments

We have investigated the trend of anodization of InSb by predeposition of a very thin Cr layer, acting as a marker. Results of Auger electron spectroscopy show that the oxidation process is carried out by oxygen in diffusion through the oxide film. The details and implications of this observation are discussed.

Characteristics of anodic native oxide MIS diodes of In 0.53 Ga 0.47 As

Anodic native oxide has been formed on In0.53Ga0.47As layers lattice-matched to InP substrate. Auger analysis of the oxide layers and capacitance/voltage characteristic measurements of MIS diodes are carried out. A U-shaped distribution of the density of surface states, the minimum of which is located at Ec-0.15 eV and is about 2.2 × 1012 cm−2eV−1, is observed.

Pulsed-laser illumination of GaAs MOS structures to study charge trapping

Trapping of both electrons and holes is investigated in the anodic native oxide of a MOS GaAs structure under pulsed bias. The density of trapped carriers, as obtained from the photo-transient response is estimated to be in the range 1011–1012 cm-2 for a low level of injection. Klectron trapping seems to be due to an injection process whereas hole trapping appears to be caused by photo-generated holes overcoming the semiconductor-oxide barrier. Like trapping af electrons, their de-trapping is attributed to a tunnelling process. Hole trapping is observed to increase with decrasing bias-pulse frequency.

Some leakage current observations on anodic native oxides on GaAs

Leakage current measurements across MOS diodes with native electrolytic nsidesevhibit a behaviour which is tentatively explained on the basis of the effect of non-oxidized As traps near the interface in the oxide,

Study of the properties of GaAs–anodic Al2O3 interfaces

For its possible use as a stable insulator passivating the surface of GaAs we have studied anodically grown Al2O3 films and their interfacial properties with GaAs. The particular aim of the passivation scheme was directed towards the neutralization of some of the long term instabilities of GaAs MeSFET’s due to the traps near the bare surface of GaAs not covered by the gate metal. Al2O3 films were grown on the surface of GaAs by the anodization of a thin film of evaporated Al in an electrolyte consisting of ammonium pentaborate and ethylene glycol. As grown, films are essentailly water free and show excellent high temperature (?800 °C) and chemical stability. The Al2O3–GaAs interface thickness was estimated to be ∠80 Å. The electrical properties of the Al2O3–GaAs interface seem to depend strongly on the type of GaAs used with superior results on p-type GaAs. However, all MOS devices showed reduced insulator charging effects compared to those employing anodic native oxides. Annealing Al2O3 on GaAs in an oxygen atmosphere at temperatures above 450 °C promotes the formation of a semi-insulating GaAs surface.

An assessment of the quality of anodic native oxides of GaAs for MOS devices

Our present understanding of the factors which affect the growth and properties of the anodic oxides of GaAs is reviewed. The various parameters which affect film composition are discussed and some new data from studies by electron spectroscopy for chemical analysis are given. An anodic growth mechanism is postulated which involves the interstitial ion drift of gallium and arsenic ions and a vacancy transport mechanism for oxygen. Experimental evidence in support of this is discussed. A brief review of the electrical properties of GaAs anodic native oxides is given. Areas in which further work is required are outlined.

Anodic native oxides on GaAs : B. Bayraktaroglu and H. L. Hartnagel. Int. J. Electron.45, (4) 337 (1978)

Anodic native oxides on GaAs : B. Bayraktaroglu and H. L. Hartnagel. Int. J. Electron.45, (4) 337 (1978)

Interface state band between GaAs and its anodic native oxide

The basic interface properties of GaAs metal-oxide-semiconductor (MOS) structures formed using an anodic oxidation process in a mixed solution of glycol and water (the AGW process) were investigated. Detailed measurements of the capacitance-voltage and conductance-voltage characteristics and the transient behaviour of the thermal and optical MOS capacitance revealed various anomalies which are not encountered in the silicon MOS system. On the basis of an analysis of such anomalies an interface state band (ISB) model is presented for the GaAs-anodic oxide MOS system, and the origin and properties of the ISB are discussed. The present ISB does not pin the surface Fermi potential but severely limits the range of its movement at steady state to the lower half of the energy gap.

Invited paper. Anodic oxides on GaAs. I. Anodic native oxides on GaAs

The anodic oxidation of GaAs is a technologically simple and a low temperature process enabling the production of reproducible high-quality native oxides on GaAs. The paper describes the influence of the GaAs properties and the best conditions for the anodic behaviour of GaAs. The initial phase of the oxide formation was also investigated in two different electrolytes. The minimum thickness of the native oxide covering the whole surface of GaAs was found to be a function of the anodic current density employed and can be as thin as 11 Å.

White-light emission from GaAs m.o.s. structures

Emission of light from GaAs m.o.s. structures with anodic native oxides is reported. The spectrum is continuous, covers the visible range and has substantial parts that have higher photon energies than the GaAs energy gap. A part of the emission therefore seems to originate from the amorphous native GaAs oxide with its wide energy gap of about 4.5 eV. The light appears white to the eye and its intensity, but not its spectral distribution, can be controlled by the bias applied to the m.o.s. structure.

Anodic oxidation of indium phosphide in glycol-based solutions

An anodic native oxide has been grown onto indium phosphide using glycol-based solutions. The variation of the anodic current behaviour with various circuit parameters has been measured, together with the thickness of the oxide as a function of voltage. MOS capacitor structures have been fabricated using this native oxide as the insulator and the I/ V and C/ V characteristics of these structures have been measured and analysed.

New anodic native oxide of GaAs with improved dielectric and interface properties

A new method of forming an anodic native oxide of GaAs with excellent dielectric and interface properties is described. The oxide is grown in a very stable and reproducible manner in an electrolyte which is a suitable mixture of (i) water, (ii) weak carboxylic acid (tartaric or citric acid), and (iii) polyhydric alcohol. The breakdown field strength of the as-grown oxide is 5×106 V/cm and the specific resistivity is 1014–1016 Ω cm. Relatively low temperature annealing in hydrogen results in greatly improved interface properties with a density of fast interface states near midgap of 1–2×1011 cm−2 eV−1, with only a small capacitance/voltage hysteresis, and only small frequency dispersion of capacitance in the accumulation region.

Electrolytic etching and electron mobility of GaAs for FET's

An electrolytic etching technique for n-GaAs is presented. The procedure is applied to post-growth etching of FET wafers to achieve uniformly thin layers from excessively thick and nonuniform material. Measurements on a Hall sample, thinned by this technique, show mobilities in good agreement with theoretical bulk mobility calculations for films as thin as 2100 Å. From Hall measurements on layers covered by the anodic native oxide, it is determined that the oxide interface traps 3·9 × 10 11 electrons per cm 2 more charge than the as-grown surface.