Transport Of Ga Research Articles

Transport and related properties of (Ga, Al)As/GaAs double heterostructure bipolar junction transistors

This paper presents a study of the transport and related properties of GaAs double heterostructure bipolar junction transistors with GaAlAs emitters and collectors utilizing both graded and abrupt junctions. By studying the temperature dependence of current-voltage characteristics, the recombination mechanisms in the transition regions associated with the base-emitter, the base-collector junction, and the quasi-neutral base region have been quantitatively separated. The junction corresponding to growth of GaAs on GaAlAs is found to have higher nonradiative recombination. For abrupt junctions, it also shows a lower barrier for electron injection than does the GaAlAs/GaAs junction. At mid-1018cm-3base doping, the junctions show ideal emission/ diffusion transport at high currents, recombination-dominated transport in a medium current range, and transport with a characteristic energy greater than twice the thermal energy at very low currents. Due to excess recombination current in the devices, the offset voltage is shown to be sensitive to the ratio of emitter and collector junction areas. At low temperatures, transport across the injecting interface of abrupt devices is dominated by tunneling and in the quasi-neutral base by diffusion. The devices exhibit gain at temperatures as low as 4.2 K. The current gain below 77 K appears to be limited by radiative recombination lifetime, and at higher temperatures by nonradiative recombination and injection efficiency. Transistors with current gains of 300 to 500 have been achieved at small emitter dimensions of 1.6 µm × 4.0 µm and at current densities exceeding 105A . cm-2. At current densities of 100 A . cm-2, some of the transistors exhibited gains approaching 100. These devices had an offset voltage of less than 100 mV. Self-aligned devices have also been fabricated and show current gains of 20 to 50 at similar dimensions. In the inverted configuration, gains of up to 50 were observed for non-self-aligned transistors. The dependence of device Characteristics upon the structure indicates that surface effects are minimal. The negative resistance exhibited by these devices at high currents is shown to be due to temperature effects resuiting from the 10-µs or lower thermal time constants.

Carrier-mediated selective transport of Ga 3+ from Ga 3+/Al 3+ binary solutions and Cu 2+ from Cu 2+/Zn 2+ binary solutions through alkylated cupferron-impregnated membrane

Selective transport of Ga 3+ and Cu 2+ was performed with a polytetrafluoroethylene membrane impregnated with long-chain alkylated cupferron (ammonium salt of N-(alkylphenyl)- N-nitrosohydroxylamine). Ga 3+ is selectively concentrated from Ga 3+/Al 3+ binary solutions and Cu 2+ from Cu 2+/Zn 2+ binary solutions with counter flow of H + in both cases.

Thermal and thermosolutal convective effects in bridgman solidification: Effect of orientation relative to gravity

A concentrated binary system (Ge-Si) and a dilute one (Ge-Ga) have been solidified at 1 g, in a new vertical Bridgman furnace where radial thermal gradients have been minimized. Very different solutal boundary layer extents ( δ Ge- Si = 3 cm, δ Ge- Ga = 2.5 mm) obtained for both systems solidified in the same thermal conditions are explained by simple analytical hydrodynamic models. It is demonstrated that : 1. The convective transport of Ga in the Ge-Ga system is due to the unavoidable residual horizontal thermal gradients associated with discontinuity of thermal properties at the solid-liquid interface. 2. The larger boundary layer extent observed for Ge-Si and the corresponding pure diffusive transport is the result of the stabilizing effect of the longitudinal solutal gradient in this system. Thus, in the case of dilute systems, convective effects can only be cancelled through a reduction of the gravity level. On the opposite, pure diffusive solute transport can be achieved in the vertical configuration a 1 g in the case of concentrated systems where a stabilizing solutal effect is operating.

Anodic oxidation of gallium arsenide

Characterisation of n-type GaAs, etched in a 5:1:1 mixture of H2SO4:H2O2:H2O, was performed using X-ray photoelectron spectroscopy (XPS) and electrochemical AC impedance. Quantitative XPS analysis of GaAs indicated that the as-received wafers had a gallium-rich native oxide which was not affected by solvent degreasing treatments. Subsequent, oxidative etching formed a thinner arsenic-rich oxide. It is suggested that etching causes initial thinning of the native oxide; subsequently, transport of Ga and As ions occurs through the film by high-field ionic conduction. Arsenic enrichment in the resultant oxide film arises from the greater mobility of Ga3+ ions compared with As3+ ions as well as the relative solubility of Ga2O3 compared with As2O3. The as-received oxide film thickness, determined from the ratio of the oxide to substrate XPS peaks, was approximately 1.1 nm. After etching this was reduced to about 0.7 nm. This thickness is consistent with the driving voltage for oxide formation being provided by the electrochemical potential difference between hydrogen peroxide and the GaAs wafer (i.e. between 0.4 V, for As, and 1.2 V, for Ga, at a nm V−1 ratio of 2). Capacitance measurements, derived from electrochemical impedance data, combined with film thickness data, gave a value of about 5 for the dielectric constant of As2O3.