Room-temperature, bottom-gate, field-effect transistor characteristics of 2D ultrathin layer GaS and GaSe prepared from the bulk crystals using a micromechanical cleavage technique are reported. The transistors based on active GaS and GaSe ultrathin layers demonstrate typical n-and p-type conductance transistor operation along with a good ON/OFF ratio and electron differential mobility.

GaS and GaSe ultrathin layer transistors.

Nanowires, sandwiched nanoribbons, and nanotubes of SnO2 are synthesized using elevated temperature synthesis techniques, and their structures are characterized in detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition to the normal rutile structured SnO2, it has been possible to form an orthorhombic superlattice-like structure in the present study. The orthorhombic structure can form in a thin nanowire, coexist with the normal rutile structured SnO2 in a sandwiched nanoribbon, or occur in the form of nanotubes. This result is distinct from that for bulk SnO2 where pressures in excess of 150 kbar are required to form the orthorhombic form. The orientation relationship between the orthorhombic SnO2 and the rutile structured SnO2 is determined to be [001]o || [102]t and (100)o || (010)t for the nanowires and sandwiched nanoribbons, and [001]o || [3 ]t and (110)o || (451)t for the nanotubes. Although the growth direction of the rutile structured SnO2 nanowires i...

Tin Oxide Nanowires, Nanoribbons, and Nanotubes

The present state of the art of transparent, electrically conducting films, with special reference to In2O3, SnO2 and Cd2SnO4, has been reviewed. Various production techniques currently in use, and typical parameters used in the processes have been discussed in detail. Electrical and optical properties of these films have been reported as a function of various parameters, e.g. substrate temperature, doping, oxygen pressure, etc. Finally, the applications of these films in research and industry have been discussed in detail.

Semiconducting transparent thin films: their properties and applications

The auger parameter, its utility and advantages: a review

The novel SnO diskettes have been synthesized by evaporating either SnO or SnO(2) powders at elevated temperature. Disregard the source material being SnO or SnO(2), the SnO diskettes are formed at a low-temperature region of 200-400 degrees C. Two types of diskette shapes have been identified: the solid-wheel shape with a drop center rim (type I) and the diskette with cone peak(s) and spiral steps (type II). The diskettes are determined to be tetragonal SnO structure (P4/nmm), with their flat surfaces being (001). The formation of the SnO diskettes is suggested to result from a solidification process. The structural evolution from SnO diskettes to SnO(2) diskettes has been investigated by oxidizing at different temperatures. The result shows that the phase transformation from SnO to SnO(2) occurs in two processes of decomposition and oxidization, and the decomposition process consists of two steps: first from SnO to Sn(3)O(4) and then from Sn(3)O(4) to SnO(2).

Growth and structure evolution of novel tin oxide diskettes.

We have studied the oxidation of layered compound GaSe with no dangling bonds on the cleaved surface using XPS and AES techniques. At room temperature, the cleaved surface is not oxidized in an oxygen atmosphere. When subjected to Ar ion sputtering, the surface starts to exhibit the behavior of metallic Ga owing to dissipation of the first sublayer of Se in the primitive layer, Se–Ga–Ga–Se. The thin layer of metallic Ga thus exposed is easily oxidized. In the thermal oxidation of cleaved GaSe in air, the oxygen diffuses into the primitive layer and combines with Ga, severing the intralayer bonding between the Se and Ga atoms. At temperature higher than 450°C, the oxygen is also intercalated between the primitive layers from the sides perpendicular to the layers. No Se oxides are observed under any of the oxidation conditions.

https://iopscience.iop.org/article/10.1143/JJAP.21.94/pdf

XPS and AES studies on the oxidation of layered semiconductor gase

The capacitance-voltage (C-V) and forward biased current-voltage (I-V) characteristics, electroluminescence (E.L) and photovoltaic effect of GaSe–SnO2 heterojunction diodes are measured. SnO2 layer is deposited on the c-plane of GaSe by using the spray method. The C-V and I-V characteristics of these diodes reveal the existence of a high resistivity layer, probably due to the diffusion of Sn into GaSe. The width of this layer is about 2.6 µm. And the current transport mechanism at low voltage is space-charge-limited. The trap density and the energy level of the trap from the valence band estimated by Lampert theory are about 5×1013~1×1014 cm-3 and 0.4~0.6 eV, respectively. The electroluminescence spectra at 275 K show one emission band due to free exciton recombination.

https://iopscience.iop.org/article/10.1143/JJAP.15.843/pdf

Electrical and Optical Properties of GaSe-SnO 2 Heterojunctions

A theory of surface excitons in molecular crystals is presented using the localized perturbation method. Conditions for the existence of surface excitons and the criterion to determine whether surface exciton states lie above or below bulk exciton states are given in terms of the enviromental shift term and the exciton transfer term within the nearest neighbour approximation. It is shown that localization energies of surface excitons are not sensitive to the crystal thickness. Densities of states for bulk and surface exciton states are calculated. The Davydov splitting of surface excitons is also evaluated.

Theory of Surface Excitons in Molecular Crystals

The depth profile of the elemental composition of the GaSe–SnO2 heterostructure has been studied by XPS and AES. The SnO2 layer was prepared by spraying a solution of SnCl4 and SbCl3 in ethyl alcohol on to the the cleaved surface of GaSe heated to ~400°C in air. After the solution had been sprayed on for about 5 secs., an SnO2 layer of thickness ~460 A formed, and a Ga2O3 layer of thickness ~120 A formed under the SnO2 layer. The Ga2O3 layer is a likely origin of the high-resistivity layer observed in the GaSe–SnO2 heterostructure.

Observation of GaSe–SnO 2 Heterostructure by XPS and AES

A theory of surface excitons in mixed molecular crystals is presented by extending the coherent potential approximation developed in the study of an infinite bulk crystal to a suitable one for a semi‐infinite crystal. The effect of the semi‐infinite nature of the crystal is taken into account by a localized perturbation method. The surface coherent potential is introduced to calculate the concent ration dependence of the energy of the surface excitons. The results give a qualitative explanation of the recent observation of surface excitons in the mixed crystal system antheracene–perdeuteroanthracene.

Shoji Ichimura

Papers

XPS and AES studies on the oxidation of layered semiconductor gase

Electrical and Optical Properties of GaSe-SnO 2 Heterojunctions

Theory of Surface Excitons in Molecular Crystals

Observation of GaSe–SnO 2 Heterostructure by XPS and AES

Surface excitons in mixed molecular crystals