A.J. Murrell

Surface chemical processes in metal organic molecular‐beam epitaxy; Ga deposition from triethylgallium on GaAs(100)

The adsorption of triethylgallium on the GaAs (100) (4×1) surface has been studied using the techniques of low energy electron diffraction, x‐ray photoelectron and Auger spectroscopies, high resolution electron energy loss spectroscopy and temperature‐programmed desorption. Condensed multilayers of the organometallic compound formed following adsorption at 150 K desorb from the surface at ∼170 K to leave a chemisorbed molecular monolayer of triethylgallium. Upon further heating this layer partially desorbs and partially decomposes to form diethylgallium in two competing processes. The diethylgallium so formed can also desorb or otherwise decompose ultimately to adsorbed Ga atoms in a reaction which results in the formation of hydrogen, ethene, and ethane. The temperature‐programmed desorption characteristics of these latter species are found to be similar to those observed for a dissociated layer of ethyl bromide. A reaction scheme is proposed to account for the observations and kinetic parameters are obt...

Surface studies of the thermal decomposition of triethylgallium on GaAs (100)

Abstract The adsorption and surface decomposition of triethylgallium (TEG) on GaAs (100) has been studied using XPS and thermal desorption techniques. TEG is found to adsorb in a molecular form on the Ga rich (4×1) surface below 150 K. As the surface temperature is raised, this molecular state dissociates to form Ga and adsorbed ethyl species. The overall cracking reaction occurs in competition with the desorption of TEG and diethylgallium (DEG). Under the conditions of our experiments the adsorbed ethyl species formed above are found to dissociate above 600 K to form mainly gas phase ethene and hydrogen with traces of ethane, resulting in the formation of a pure Ga layer within the sensitivity limits imposed by XPS.

Surface studies of the interaction of Cl2 with InP(100)(4 × 2); an investigation of adsorption, thermal etching and ion beam assisted processes

The reactions of chlorine on the InP(100)(4 × 2) surface have been investigated using LEED, AES and TDS techniques. Chlorine forms a strongly bound chemisorbed monolayer on the semiconductor surface during low gas exposures. At high gas exposures, bulk corrosion sets in and an In-rich chloride film is formed at the interface which desorbs as InCl 3 . The degree of surface segregation which takes place is found to depend on the chlorine dosing pressures employed and the chemistry exhibited is also very sensitive to the state of the semiconductor surface; on In enriched interfaces corrosion takes place some 300 times more rapidly and InCl rather than InCl 3 is the desorbing product. The surface transformations brought about by low energy ion beams are investigated. Ion beam irradiation sputters InCl and P 4 from the chloride layer and converts the chloride rich corrosion scale into InCl. A mechanism for ion beam assisted etching is proposed and the results compared to previous studies.

An investigation of the adsorption and decomposition of PH3 and NH3 on GaAs(100)

Abstract The adsorption and thermal decomposition of PH 3 and NH 3 on the Ga-rich GaAs(100)-(4 × 1) surface has been studied using temperature programmed desorption (TPD), Auger electron spectroscopy (AES) and high resolution electron loss spectroscopy (HREELS) techniques. At room temperature PH 3 was found to chemisorb on the GaAs surface and HREELS and isotopic scrambling experiments using deuterium suggest the major species present is PH 2 . Electron beam irradiation brings about complete dissociation to form phosphorus on the surface which is stable for temperatures up to 800 K, at which point desorption of P 4 takes place. Adsorption at 140 K shows three adsorption states. At low coverages adsorption into two chemisorbed PH 2 states occurs; at higher coverages a molecularly bound PH 3 state exists which reversibly desorbs at low temperatures as the temperature is raised. Adsorption of NH 3 at 150 K yields two clearly resolved NH 3 desorption peaks. However, HREELS indicates that both arise as a result of molecular adsorption state. The lower temperature peak is due to the physisorbed state while the higher temperature peak (250–350 K) is associated with desorption of the chemisorbed phase. Some thermal cracking of NH 3 on the surface takes place giving rise to NH 2 and H species as shown by HREELS and coadsorption experiments with deuterium. These species undergo recombinative desorption at high temperatures although trace amounts completely decompose to produce surface N. Electron beam irradiation at energies as low as 10 eV was also observed to result in decomposition of the adsorbed molecular phases.

Surface decomposition mechanism of the novel precursor bistrimethylamine aluminium hydride on GaAs(100)

Abstract The surface decomposition mechanism of bistrimethylamine aluminium hydride [(Me3N)2 · AIH3] on the Ga-rich (4 × 1) GaAs (100) surface is studied by TDS, HREELS and XPS. It is found that the first monolayer of the complex chemisorbs molecularly at 150 K. The decomposition pathway is shown to involve the activated dissociation of this chemisorbed precursor to produce Al, adsorbed H atoms and trimethylamine. The latter species desorb without further fragmentation and this key feature results in the deposition of carbon-free aluminium films. This contrasts markedly with the decomposition of organometallics like trimethyl aluminium (TMA) which are traditionally used in Al CVD where carbon incorporation is an intrinsic part of the decomposition process.

The thermal decomposition of triethylgallium on GaAs(100)

Abstract The adsorption and thermal decomposition of triethylgallium (TEG) on GaAs has been studied using thermal desorption and XPS techniques. Pure Ga films are deposited when adsorbed TEG layers on GaAs are heated in a reaction which competes with TEG and diethylgallium (DEG) desorption. Ethene, ethene and hydrogen are detected as the decomposition products of the overall cracking reaction.

The adsorption and thermal decomposition of PH3 and NH3 on GaAs(100)

The adsorption and thermal decomposition of PH3 and NH3 on the Ga-rich GaAs(100)-(4*1) has been studied using temperature programmed desorption, isotope exchange reactions and high resolution electron energy loss spectroscopy (HREELS). At 120 K PH3 adsorbs molecularly while HREELS and isotope exchange reactions with deuterium suggest that PH2 is the major species present at 300 K. Molecular adsorption is also observed for NH3 at 150 K when both the physisorbed and chemisorbed states are formed. HREELS and isotope exchange reactions show that dissociation of the molecular state to form NH2 occurs when the adsorbed phase is heated.

Surface Reaction Mechanisms in the Metallisation and Etching of Semiconductor Materials.

Surface spectroscopic techniques have been used to investigate aluminium deposition form tri-methyl aluminium (TMA) on Si(100), and the etching of InP by chlorine. Thermal reactions and processes stimulated by UV lamps and ion beams are examined. The results are interpreted in the light of the adsorption states which are formed and the surface transformations of chemical states which are observed to occur.

Thermal and ion-beam-induced etching of InP with chlorine

Surface spectroscopic techniques have been used to investigate adsorption and thermal and ion-induced processes at the InP(100)-Cl2 interface. Two adsorption states are identified and etching reactions are interpreted in terms of surface chemical transformations and desorption processes involving these states.