X-ray induced, substrate-carrier mediated deposition of metal on GaAs (original) (raw)

Wet etching of GaAs using synchrotron radiation x rays

Journal of Applied Physics, 2001

A room-temperature photoenhanced chemical wet etching process for n-type GaAs using x rays from a synchrotron radiation source is described. HNO 3 :H 2 O was used as the etching solution. This process produces smoothly etched surfaces on n-GaAs with a root-mean-square surface roughness of 0.7-2.0 nm, which compares favorably to the unetched surface roughness ͑0.4 nm͒. Dependence of the etching rate on x-ray intensity and energy, solution concentration, and semiconductor doping type are reported.

Utilization of wet chemical etching for revealing defects in GaAs X-ray detector arrays

Vacuum, 2005

The aim of the study was to check the potential of wet chemical etching to improve the performance of GaAs-based X-ray detector arrays in view of their applications in medical diagnostics and nondestructive evaluation. The paper presents results of tests provided on SI GaAs detector arrays of different pixel sizes. The characterization of detector parameters was performed by current-voltage measurements and electron microscopy. The effect of MESA etching on the electrical device properties of reverse breakdown voltage and current density increases with decreasing pixel size. Irregular subsurface leakage current paths between individual pixels have been revealed by defect-selective shallow etching. r

Sample size effect in photoelectrochemical etching of n-GaAs

Applied Physics Letters, 2000

A sample size effect on the etching rate in the photoelectrochemical etching of n-GaAs is demonstrated using synchrotron radiation x rays as the light source. It is shown that the etching rate increases significantly with the ratio of sample size to x-ray illuminated area. The rate-limiting effect on the charge transfer across the semiconductor-electrolyte junction is found to account for the phenomenon. It is also found that the etching rate relates to the nonilluminated area with a rather simple function.

Characterization of wet-etched GaAs (100) surfaces

Surface and Interface Analysis, 2005

To enable the use of GaAs-based devices as chemical sensors, their surfaces must be chemically modified. Reproducible adsorption of molecules in the liquid phase on the GaAs surfaces requires controlled etching procedures. Several analytical methods were applied, including Fourier transform infrared spectroscopy (FTIRS) in attenuated total reflection and multiple internal reflection mode (ATR/MIR), high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) for the analysis of GaAs (100) samples treated with different wet-etching procedures. The assignment of the different features due to surface oxides present in the vibrational and XPS spectra was made by comparison with those of powdered oxides (Ga 2 O 3 , As 2 O 3 and As 2 O 5 ). The etching procedures here described, namely, those using low concentration HF solutions, substantially decrease the amount of arsenic oxides and aliphatic contaminants present in the GaAs (100) surfaces and completely remove gallium oxides. The mean thickness of the surface oxide layer drops from 1.6 nm in the raw sample to 0.1 nm after etching. However, in presence of light, water dissolution of arsenic oxides is enhanced, and oxidized species of gallium cover the surface.

Local oxide growth on the n-GaAs surface studied by small area XPS

Surface Science, 1999

The photoanodic dissolution of n-GaAs was investigated in a buffered solution at an intermediate pH (pH 9). At this pH, the GaAs dissolution rate was limited by the growth of an anodic oxide film. A laser illumination leads to a local oxide growth only in the illuminated part on to GaAs. Transient photocurrent and capacitance measurements clearly show dissolution kinetics in two steps: the first step is about a few tens of seconds and is correlated with gallium oxide dissolution, and the second step is greater than a few minutes, indicating the origin of at least two surface films onto GaAs. A parallel approach using in-situ electrochemistry and ex-situ surface analysis ( XPS ) was performed to characterise the growth of an anodic film on to GaAs. A gallium enrichment was detected on this oxide film. The arsenic deficiency in this oxide results from a higher arsenic oxide solubility. The limitation of the GaAs dissolution is due to the dissolution of gallium oxide at pH 9. (I. Gérard) etching profiles were observed under a laser-beam 0039-6028/99/$ -see front matter

Low-energy particle treatment of GaAs surface

Thin Solid Films, 2003

Modification of high-doped GaAs surface by the interaction with RF plasma and a monoenergetic beam of similar chemical composition (Ar with a low content of H ) was investigated via the evolution of optical, electrical and structural properties. A 2 reduction in the free charge concentration in the GaAs surface region of ;100 nm in thickness is concluded from Raman spectroscopy. In the processed samples, the surface electric field strength induced by a laser beam (photoreflectance technique) continually decreases with both the energy and fluence of impinging particles. The same results were obtained by evaluation of quasistatic C-V curves of corresponding MOS structures. They confirmed that longer exposure caused the formation of ;100nm-thick modified near-surface region with a decreased donor concentration. After the plasma irradiation, an ;10-nm-thick outermost insulating layer was created in situ. The formation of textured polycrystalline grains with (100) orientation in the surface region was observed by X-ray diffraction. ᮊ

High-Resolution X-ray Photoelectron Spectroscopy of Chlorine-Terminated GaAs(111)A Surfaces

Journal of Physical Chemistry B, 2006

Oxide-terminated and Cl-terminated GaAs(111)A surfaces have been characterized in the As and Ga 3d regions by high-resolution, soft X-ray photoelectron spectroscopy. The Cl-terminated surface, formed by treatment with 6 M HCl(aq), showed no detectable As oxides or As 0 in the As 3d region. The Ga 3d spectrum of the Cl-terminated surface showed a broad, intense signal at 19.4 eV and a smaller signal at 21.7 eV. The Ga 3d peaks were fitted using three species, one representing bulk GaAs and the others representing two chemical species on the surface. The large peak was well-fitted by the bulk GaAs emission and by a second doublet, assigned to surface Ga atoms bonded to Cl, that was shifted by 0.34 eV from the bulk GaAs 3d emission. The smaller peak, shifted by 2.3 eV in binding energy relative to the bulk GaAs Ga 3d signal, is assigned to Ga(OH) 3. The data confirm that wet chemical etching allows for the formation of well-defined, Cl-terminated GaAs(111)A surfaces free of detectable elemental As, that can provide a starting point for further functionalization of GaAs.

Implication of X-ray photoelectron intensities for a layer model of GaAs surface

Journal of Electron Spectroscopy and Related Phenomena, 1985

Intensities of X-ray photoelectron transitions from the As 3d level are theoretically analysed taking into account many-electron interactions. The latter interactions profoundly affect the relative intensities of the transitions as well as binding energies. Implications for the surface structure of GaAs are then discussed and in particular we show that As atoms having the same chemical environment are spread over distances into the surface comparable to the interatomic spacing. This supports a recently proposed layer model for the untreated surface of GaAs.

Angle-resolved XPS structural investigation of GaAs surfaces

Journal of Crystal Growth, 2008

Angle-resolved X-ray photoelectron spectroscopy (ARXPS) analysis has been performed on GaAs (1 0 0) surfaces in different conditions as naturally oxidized, Ar + ion sputtering (E ¼ 1-5 keV) and chemical etching in H 2 SO 4 /H 2 O 2 /H 2 O (3:1:1). The most sensitive angle to the surface compositional changes was the take-off angle (TOA): 251. Native oxide phases on GaAs consist of a mixture of Ga 2 O 3 , As 2 O 3 and As 2 O 5 . Ar + ion sputtering procedure modifies the surface composition, in the altered layer where the concentration ratio C Ga /C As tends to 1.5-1.6. Wet chemical etching removes the oxide layer and the As-rich region from the surface. In the experiment combining chemical etching with Ar + ion sputtering for cleaning purpose, the native oxides are removed from the surface and C Ga /C As tends to stoichiometry. The experiment on native oxide reconstruction after storage in high-vacuum conditions (p$10 À8 Torr) provides evidence of the high reactivity of GaAs (1 0 0) surfaces. We have observed the presence of an As oxide (BE ¼ 43 eV) within a concentration range of 2-3%. r