A surface analytical study of GaAs(100) cleaning procedures (original) (raw)
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Surface chemistry and Fermi level movement during the self-cleaning of GaAs by trimethyl-aluminum
Applied Physics Letters, 2011
The removal of the native oxides from NH4OH--cleaned p--GaAs (100) by exposure to trimethyl--aluminum (TMA) was studied by in situ photoelectron spectroscopy using synchrotron radiation. The reduction of high--valence As--and Ga--oxides occurred through different routes: while As 3+ was reduced to As (1±Δ)+ suboxides (with 0≤Δ≤1), Ga 3+ was directly removed. The surface Fermi level was shifted by about 100 meV towards the valence band edge upon TMA exposure. This indicates that removing the native oxide of GaAs by TMA is insufficient to create interfaces between GaAs and Al2O3 with defects densities below the 10 12 cm --2 range.
GaAs clean up studied with synchrotron radiation photoemission
IOP Conference Series: Materials Science and Engineering, 2012
In this contribution we describe the chemical changes at the surface of GaAs upon adsorption of tri-methyl-aluminum (TMA). TMA is used to grow Al 2 O 3 with atomic layer deposition (ALD) usually using H 2 O as oxygen source. Recently, it was pointed out that the adsorption of TMA on various III-V surfaces reduces the native oxide, allowing the growth of an abrupt III-V/High-K interface with reduced density of defects. Synchrotron radiation photoemission spectroscopy (SR-PES) is a powerful method to characterize surfaces and interfaces of many materials, as it is capable to determine their chemical composition as well as the electronic properties. We performed in-situ SR-PES measurements after exposing a GaAs surface to TMA pulses at about 250°C. Upon using the possibility of tuning the incident photon energy we compared the Ga3d spectra at 41 eV, 71 eV, 91 eV and 121 eV, as well as the As3d at 71 eV and 91 eV. Finally, we show that using SR-PES allows a further understanding of the surface composition, which is usually not accessible with other techniques.
GaAs interfacial self-cleaning by atomic layer deposition
Applied Physics Letters, 2008
The reduction and removal of surface oxides from GaAs substrates by atomic layer deposition ͑ALD͒ of Al 2 O 3 and HfO 2 are studied using in situ monochromatic x-ray photoelectron spectroscopy. Using the combination of in situ deposition and analysis techniques, the interfacial "self-cleaning" is shown to be oxidation state dependent as well as metal organic precursor dependent. Thermodynamics, charge balance, and oxygen coordination drive the removal of certain species of surface oxides while allowing others to remain. These factors suggest proper selection of surface treatments and ALD precursors can result in selective interfacial bonding arrangements.
High resolution photoemission yield study of the GaAs(100) surface cleaned by atomic hydrogen
2005
High-resolution photoemission yield spectroscopy (PYS) has been used to study the electronic properties of space charge layer of the real GaAs(100) surface cleaned by atomic hydrogen. The ionization energy, work function and interface Fermi level position were determined as a function of hydrogen dose. Moreover, the evolution of effective density of filled electronic states localized in the band gap and in the upper part of the valence band was observed. Our experiments showed that for the hydrogen dose up to 10 4 L H 2 the contamination etching stage occurs for which the interface Fermi level position E F-E v reaches a value of 1.06 eV. For the higher hydrogen dose at the level 10 5 L H 2 the interface Fermi level position E F-E v reaches a value of 0.75 eV which corresponds to the degradation of GaAs(100) surface that becomes covered by metallic Ga.
H plasma cleaning and aSi passivation of GaAs for surface channel device applications
Journal of Applied Physics, 2009
We discuss GaAs͑001͒ cleaning and surface passivation for metal-oxide-semiconductor capacitors and field effect transistors fabricated with HfO 2 as high-gate oxide. An amorphous-Si passivating layer is deposited by molecular beam deposition on a 2 ϫ 1 reconstructed GaAs surface cleaned using a remote rf H plasma. The H plasma effectively removes C contaminants from the surface, but a progressive Ga enrichment and the presence of Ga-O bonds are observed. The capacitance-voltage measurements on capacitors under peripheral illumination show inversion, which is an indication of a passivated interface. The D it distribution as function of energy in the band gap is extracted by using the conductance technique at high and low temperatures and is reported for HfO 2 / a-Si gate stacks on H-cleaned GaAs. The observed D it distribution is asymmetric. Values as low as 7 ϫ 10 11 eV −1 cm −1 are found in the upper half of the band gap. One clear peak at 0.7 eV and a tail at 0.2 eV above the valence band maximum, which can be part of a second peak, are also observed. Transistor data confirm that a conducting channel is effectively opened at or very close to the GaAs surface.
Surface passivation and morphology of GaAs(100) treated in HCl-isopropanol solution
Applied Surface Science, 2004
A promising chemical surface preparation technique, which consists in the treatment of GaAs(1 0 0) in HCl-isopropyl alcohol (HCl-iPA) solution under nitrogen atmosphere, is further developed. It was shown earlier [Tereshchenko et al., J. Vac. Sci. Technol. A 17 (1999) 2655] that HCl-iPA treatment and subsequent anneals in vacuum yielded atomically clean GaAs(1 0 0) surface with the whole range of surface reconstructions characteristic of this crystal face. In the present work the mechanisms of the passivation of GaAs(1 0 0) surfaces by arsenic overlayers as a result of HCl-iPA treatment are experimentally studied by X-ray photoelectron spectroscopy, low-energy electron diffraction and atomic force microscopy. The HCl-iPA treatment of clean As-stabilized GaAs(1 0 0) surfaces results in chemical passivation of the surface by submonolayer amount of excess arsenic. For the initially oxidized surfaces the treatment leads to the formation of 1-3 monolayers of amorphous arsenic on the surface, with the major part of the arsenic originating from the surface oxides dissolved in HCl-iPA. The HCl-iPA treatment preserves the atomic flatness of the GaAs(1 0 0) surface, keeping the mean roughness on a very low level of approximately $0.1 nm.
Hydrogen radical surface cleaning of GaAs for MBE regrowth
Journal of Crystal Growth, 1997
Modulation-doped GaAsiAlGaAs two-dimensional electron gas (2DEG) structures have been regrown on air-exposed GaAs buffer layers, at varying proximity to the regrowth interface. The degradation in 2DEG quality with decreasing separation from a hydrogen radical (H*) cleaned regrowth interface was found to be much reduced in comparison to that for a thermally cleaned interface. H* cleaning has allowed for the growth of a 2DEG lying only 50 nm from the regrowth interface with a mobility, after illumination, of 5.3 x lo5 cm2 V-' sm 1 at a carrier concentration of 4.2 x 10' ' cm-2, SIMS characterisation has been used to measure significant reductions in contamination at the regrowth interface at cleaning temperatures of 500'C. Cathodoluminescence data, measured for a 5 nm quantum well lying 30 nm from the regrowth interface, further indicate the improved growth morphology achieved following H* cleaning, in comparison to that achieved by thermal decontamination.
Journal of Applied Physics, 2006
We report on aging and detergent washing effects in GaAs wafers passivated with hexadecanethiol ͑HDT͒ ͓HS͑CH 2 ͒ 15 CH 3 ͔. The evolution of the photoluminescence ͑PL͒ signal from GaAs was measured at room temperature as a function of time, up to 1000 h, for thiolated ͑001͒ GaAs that was solvent cleaned and etched using standard procedures, and for thiolated ͑110͒ GaAs that was obtained by cleaving in air. For 2 h of thiolation time, the decay of the PL signal from ͑001͒ GaAs and ͑110͒ GaAs could be fitted, respectively, with double and single exponential functions. This indicates that at least two different types of non-adiative recombination centers ͑NRRC͒ form on the ͑001͒ surface. The overall density of surface states formed on ͑110͒ GaAs is significantly lower than those on ͑001͒ GaAs. A single exponential decay of the PL signal has been observed for 18 h thiolated samples. The strong increase of the PL signal after detergent washing of ͑001͒ GaAs suggests that this treatment is effective in removal of some of the NRRC. The 19-fold enhancement of the PL signal, in comparison to that of the oxidized sample, has been obtained using the sample that, following the etching and detergent washing procedures, was thiolated with HDT.
Composition and structure of chemically prepared GaAs(111)A and (111)B surfaces
Surface Science, 2006
The (1 1 1)A and (1 1 1)B surfaces of GaAs chemically treated in HCl-isopropanol solution (HCl-iPA) and annealed in vacuum were studied by means of X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED) and electron energy loss spectroscopy (EELS). To avoid uncontrolled contamination, chemical treatment and sample transfer into UHV were performed under pure nitrogen atmosphere. The HCl-iPA treatment removes gallium and arsenic oxides, with about 0.5-3 ML of elemental arsenic being left on the surface, depending on the crystallographic orientation. With the increase of the annealing temperature, a sequence of reconstructions were identified by LEED: (1 · 1) and (2 · 1)B surface. These sequences of reconstructions correspond to the decrease of surface As concentration. The structural properties of chemically prepared GaAs(1 1 1) surfaces were found to be similar to those obtained by decapping of As-capped epitaxial layers.
Investigation of neutralized (NH[sub 4])[sub 2]S solution passivation of GaAs (100) surfaces
Applied Physics Letters, 1997
Synchrotron radiation photoelectron spectroscopy combined with scanning electron microscopy ͑SEM͒ and gravimetry has been used to study GaAs ͑100͒ surfaces treated with a neutralized ͑NH 4 ͒ 2 S solution. Compared to the conventional basic ͑NH 4 ͒ 2 S solution treatment, a thick Ga sulfide layer and strong Ga-S bond were formed on the GaAs surface after dipping GaAs wafers in a neutralized ͑NH 4 ͒ 2 S solution. Gravimetric data show that the etching rate of GaAs in the neutralized ͑NH 4 ͒ 2 S solution is about 15% slower than that in the conventional ͑NH 4 ͒ 2 S solution. From SEM observation, fewer etching pits with smaller sizes were found on the neutralized ͑NH 4 ͒ 2 S-treated GaAs surface. © 1997 American Institute of Physics. ͓S0003-6951͑97͒01247-3͔