Jia-Fa Fan

Universal Passivation Effect of (NH4)2Sx Treatment on the Surface of III-V Compound Semiconductors

The effectiveness of (NH4)2Sx treatment on the (100) surface of GaP, (Al, Ga)As, InP and InAs was studied in comparison to that on GaAs by means of Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED). It was concluded that the existence of sulfur atoms bonded to semiconductors prevents the adsorption of oxygen. This phenomenon brings about the metal-dependent Schottky barrier fabricated on the (NH4)2Sx-treated surfaces, implying the reduction in the interface state density. The structure and effect of the (NH4)2Sx-treated surface of III-V compounds are qualitatively the same.

The Effect of (NH4)2S Treatment on the Interface Characteristics of GaAs MIS Structures

MIS capacitors prepared on the (NH4)2S-treated GaAs substrate showed a marked reduction in the density of the dominant pinning levels near 0.6 eV below the conduction band. The annealing effect on the interface characteristics was also investigated. Analyses by means of secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) indicate that sulfur atoms at the interface stabilize the oxygen-free GaAs surface both electronically and thermally.

Metal-Dependent Schottky Barrier Height with the (NH4)2Sx-Treated GaAs

Schottky barriers have been prepared on (NH4)2Sx-treated GaAs. The barrier height was observed to change remarkably with the kind of metals, which is predicted in the case of low interface state density. We found that the interface trap density was reduced to 9.8×1012 cm-2eV-1 by the treatment from 6.5×1013 cm-2eV-1 for the untreated one.

Studies on an (NH4)2Sx-Treated GaAs Surface Using AES, LEELS and RHEED

Surface properties of (NH4)2Sx-treated GaAs (100), (111)Ga and ()As planes were studied by means of Auger electron spectroscopy (AES), low-energy electron energy loss spectroscopy (LEELS) and reflection high-energy electron diffraction (RHEED). We found that oxide-free and sulfur-terminated GaAs surfaces produced by the (NH4)2Sx treatment provided the reduction of interface state density. Furthermore, comparison of various planes revealed that (i) sulfur atoms could combine with both Ga and As and (ii) bonding between Ga and S was stronger than that between As and S.

Marked Reduction of the Surface/Interface States of GaAs by (NH4)2Sx Treatment

MIS capacitors have been fabricated on (NH4)2Sx-treated GaAs using a SiOx insulator prepared by conventional resistive-heating evaporation. The MIS interface state density was found to be about 1.2×1011 cm-2·eV-1 in a wide range of the band gap, which is two orders of magnitude less than that on the as-etched GaAs.

Epitaxial growth of Al on (NH4)2Sx-treated GaAs

Epitaxial growth of Al film on the (NH4)2Sx-treated surface of (100) GaAs was investigated by means of reflection high-energy electron diffraction (RHEED). A single crystal of epitaxial (110) Al film was obtained on the treated surface with heat treatment at 300°C prior to Al deposition, while Al film became polycrystalline without heat treatment. The effect is explained in terms of the alignment of S atoms on GaAs. The (NH4)2Sx-treated surface seems to be useful in the wide range of GaAs processes.

AES Observation on the Photochemically Washed Surface of GaAs

A GaAs surface prepared by photochemical washing (PCW) has been studied by means of AES. We found that improvement and degradation in the PL intensity on the treated surface were related to the removal and reaccumulation respectively, of excess As in the surface oxide. The effect for passivation of the GaAs surface by PCW is found to be temporary and unreliable.

Stabilization of GaAs Surface/Interface by Sulfur Treatment

Stabilization of the GaAs surface/interface by the (NH4)2S treatment has been in_ vestigaLed. Enhancement of Photoluminescence intensity-ufd drast.ic improvement of Capacitance-Voltage characteristics on metal-insulator-iemiconductor(MIS) structures prepared by this treatment lead to the reduction of surface recombi.nation velocity and surface state density. Auger electron spectroscopy and 1ow-energy electron energy loss spectroscopy indicate that the removal of oxide or As on the surface and the passivation of the GaAs surface by one monoatomic Sulfur 1ayer.