Shinichiro Takatani

Thermal stability of WSix/GaAs interface

Secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS), and measurements of forward current‐voltage characteristics at various temperatures were used to study metallurgical reactions in WSix/GaAs formed by sputter deposition. Both SIMS and RBS showed that annealing at 800 °C results in migration of W and Si into GaAs when the atomic ratio x deviates from 0.5. On the other hand, the forward current‐voltage characteristics of WSix/GaAs diodes at various temperatures showed that the excess current across the interface induced after annealing is large when x deviates substantially from 0.5, in agreement with the SIMS and RBS results. It is suggested that the migration of W and Si is directly involved in the thermal degradation of the structural and electrical properties of the WSix/GaAs interface and its x dependence.

Pt/PbZrxTi1−xO3 interfacial reaction and Schottky barrier formation studied by x-ray photoelectron spectroscopy: Effect of H2 and O2 annealing

The Pt/PbZrxTi1−xO3 (PZT) interfacial reaction caused by low-temperature (320 °C) annealing and resulting change in the surface Fermi level position (Schottky barrier height) has been studied by using in vacuo x-ray photoelectron spectroscopy (XPS). A thin (2 nm) Pt layer was deposited on a polycrystalline PZT film and annealed in 0.5-Torr H2 and O2 in a chamber connected to the XPS chamber. For the PZT samples annealed prior to Pt deposition, a small amount of metallic Pb was produced after the Pt deposition. The annealing also moved the surface Fermi level (EF) at the Schottky interface toward the conduction band minimum (EC) of PZT by 0.4 eV, as evidenced by the band-bending shift of the PZT core levels. Excess metallic states appeared in the valence-band spectra of an annealed bare PZT surface. There was no appreciable annealing-atmosphere dependence in the amount of metallic Pb produced and surface EF position at the PT/PZT interface. However, a clear annealing-atmosphere dependence was observed for ...

Atomic hydrogen cleaning of GaAs and InP surfaces studied by photoemission spectroscopy

Abstract Cleaning of GaAs and InP surfaces by atomic hydrogen (H∗) beam irradiation was investigated using synchrotron radiation photoemission spectroscopy and Auger electron spectroscopy. The surfaces were irradiated by a H∗ beam generated by a hot tungsten tube at a sample temperature of 360°C. After the H∗-beam irradiation, the GaAs and InP surfaces exhibited a streaky (2 × 1) and (2 × 4) RHEED pattern, respectively. It took a longer irradiation time to clean the InP surface than the GaAs surface. Photoemission spectroscopy revealed that the most persistent oxide in the H∗ cleaning process is Ga 2 O 3 for the GaAs surface, and In(PO 3 ) 3 for the InP surface.

Effect of H2 Annealing on a Pt/PbZrxTi1-xO3 Interface Studied by X-Ray Photoelectron Spectroscopy.

The chemical reaction and the change in the Schottky barrier height at the Pt/PbZrx Ti1-x O3 (PZT) interface as a result of annealing was studied by in-vacuo X-ray photoelectron spectroscopy. Annealing at 320° C produced metallic Pb atoms which migrated on the Pt surface. There were more of these atoms when the annealing was done in H2 than in a vacuum. After H2 annealing, the core level peaks for the elements in the PZT showed a band bending shift of ~0.4 V toward higher binding energy, indicating that the n-type Schottky barrier height at the Pt/PZT interface was lowered by the H2 annealing.

Passivation of InP-Based Heterostructure Bipolar Transistors in Relation to Surface Fermi Level

The effect of surface Fermi level position on dc-characteristics of InP-based heterostructure bipolar transistors (HBT) is reported. The Fermi level of an InP surface covered with silicon oxide was located at an energy position close to the conduction band minimum of InP. This implies that an electron accumulation layer forms at the interface, which acts as a surface leakage path. The HBT passivated with silicon oxide films showed large excess base current and poor current gain. In contrast, the Fermi level position at the silicon nitride/InP interface was found to be near the midgap, and no electron accumulation layer was formed at the interface. The HBT passivated with silicon nitride film showed excellent dc characteristics with very small, excess base current.

Evidence of Ga2Se3-Related Compounds on Se-Stabilized GaAs Surfaces

A Se-stabilized GaAs(001) surface is examined by extended X-ray absorption fine structure (EXAFS) analysis. The Se K-edge EXAFS shows components due not only to the first but also the second nearest neighbors, indicating that the Se atoms are incorporated into ordered atomic arrangements. Comparing the interatomic distances to those measured for Ga2Se3 and GaSe, it is concluded that the nature of the surface compound on the Se-stabilized GaAs surface is close to that of Ga2Se3.

Generation mechanism of gate leakage current due to reverse-voltage stress in i-AlGaAs/n-GaAs HIGFETs

Device degradation characterized as an increase in the gate leakage current due to continuous reverse-voltage stress was investigated for a 0.35-/spl mu/m WSi gate i-AlGaAs/n-GaAs doped channel HIGFET (heterostructure insulated-gate field-effect transistor). The gate leakage current, which was dominated by a hole current generated by impact ionization, was found to increase after the application of a gate-to-drain voltage of -6 V for a certain period. The occurrence of the impart ionization was evidenced by the generation of a substrate current and by the negative temperature coefficient of the gate current. The degradation was retarded at an elevated temperature, indicative of hot-carrier-related degradation. The degraded device also showed an ohmic-like gate leakage current. Subsequent annealing at temperatures above 300/spl deg/C significantly restored the current-voltage (I-V) characteristics. From these observations, a degradation model was developed in which hot holes generated by impact ionization are trapped in the insulator/semiconductor interface, contracting the surface depletion region and thereby increasing the electric field near the gate-edge. A surface treatment using CF/sub 4/ plasma was used to suppress the degradation. An FET fabricated using this treatment showed a remarkable decrease in degradation.

Electronic properties of Se-treated SiO2/GaAs interfaces

GaAs metal‐insulator‐semiconductor diodes with a Se‐treated interface and photochemical‐vapor‐deposited SiO2 are investigated. The diodes show little frequency dispersion in the capacitance at any accumulation bias, only a few percent between 1 kHz and 1 MHz. Analysis using Terman’s method shows that the density of interface states near the midgap is drastically reduced. In addition, insertion of a Se‐treated AlGaAs thin layer at the insulator/semiconductor interface is found to reduce the number of interface states near the conduction band minimum. These improved characteristics are preserved after annealing to 400 °C.

Excimer laser assisted etching of AlGaAs and GaAs

Laser assisted etching of AlGaAs and GaAs by chlorine using ArF and KrF excimer lasers was investigated. The etching rate of AlGaAs was shown to be larger than that of GaAs. Quadrupole mass spectroscopy analysis of the etching products for KrF assisted etching showed intense Ga+ and As+ signals from AlGaAs. It is suggested that a laser‐induced neutral atom desorption process is enhanced in the AlGaAs etching. Hall measurements of a shallow channel heterostructure sample and GaAs Schottky diode characterization demonstrated the low damage of the etching process. The etching profile was examined by scanning electron microscopy and feasibility for field effect transistor gate recess etching was shown.

Digital etching of GaAs using Se molecular beam and atomic hydrogen beam

A novel digital etching technique for GaAs was investigated. The GaAs surface was first irradiated by a Se molecular beam to form Ga2Se3 on the surface as a result of the Se–As exchange reaction. The surface was then irradiated by an atomic hydrogen (H*) beam to selectively etch the Ga2Se3 layer. These steps were repeated until etched to the desired depth. An etch rate of about 0.2 nm/cycle was obtained at the substrate temperature of 500 °C. The etch rate was nearly independent of the Se and H* irradiation time, suggesting the involvement of a self‐limiting mechanism in the etching process.