M. Stam

Electrical properties of GaSb Schottky diodes and p-n junctions

Abstract The electrical properties of Schottky diodes and p-n junctions on GaSb ((100), doped with 2 × 10 17 cm −3 tellurium) were examined. Capacitance-voltage measurements at 300 K show barrier heights of0.65 eV (Al), 0.6 eV (Au, In, Pd), 0.5 eV (Ga) and 0.42 eV (Sb). The barrier heights tend to track the band gap increase as the temperature is lowered. Forward I-V characteristics of the GaSb Schottky diodes at 300 K have ideality factors in the range 1.9–2.4, indicating that generation-recombination current from a near midgap center is dominating the behavior. At room temperature and below, the activation energy for J s in the expression J=J s exp (qV/nkT) is 0.24 eV. However, at higher temperatures the activation energy becomes more nearly equal to the barrier height as deduced from C-V measurements and the n value decreases below two. Deep level transient spectroscopy (DLTS) measurements reveal the presence of one electron trap with a concentration around 10 15 cm −3 at 0.25 eV below the conduction band edge. Electron beam induced current (EBIC) measurements give an electron diffusion length of 1.3 μm. In GaSb p-n + junctions grown by molecular beam epitaxy, DLTS measurements show the presence of a generation-recombination center at E v +0.33 eV with a concentration of 5×10 14 cm −3 . The effective lifetime inferred from the saturation current value is around 2×10 −9 s. For reverse bias, the mechanism of breakdown at large voltages in p-n + structures includes tunneling via local centers with an energy of around 0.3 eV. Forward and reverse characteristics can be improved by (NH 4 ) 2 S treatments for both Schottky barriers and pn + junctions.

Hydrogen treatment effect on shallow and deep centers in GaSb

It is shown by spreading resistance and capacitance–voltage measurements that atomic hydrogen passivates shallow acceptors and donors in GaSb. Deep level passivation by hydrogen also occurs, as revealed by deep level transient spectroscopy measurements on Schottky diode structures. Effective diffusion coefficients for hydrogen were determined for both n+ and p+ GaSb; in the former case the diffusion is thermally activated with the relationship DH=3.4×10−5e−0.55 eV/kT, whereas in p+ material DH=1.5×10−6e−0.45 eV/kT over the temperature range 100–250 °C. Reactivation of passivated shallow and deep levels occurs for temperatures of 250–300 °C.

High‐resistivity GaAs grown by high‐temperature molecular‐beam epitaxy

It is shown that when grown by molecular‐beam epitaxy at high temperatures around 700 °C, undoped GaAs layers display high resistivity. Preliminary results seem to imply that Ga‐related inclusions that produce internal Schottky diodes might be responsible for this effect rather than the presence of deep centers. It is proposed that Ga‐related inclusions that produce internal Schottky diodes might possibly be responsible for this effect rather than the presence of deep centers.

Schottky barriers of various metals on Al0.5Ga0.5As0.05Sb0.95 and the influence of hydrogen and sulfur treatments on their properties

Schottky barriers of Au, Al, and Sb on n‐ and p‐type layers of Al0.5Ga0.5As0.05Sb0.95 have been studied. The Schottky barriers are high for Au (1.3 eV) and Al (1.2 eV) deposited on n‐type material and very low for these metals on p‐type layers. The behavior of Sb is unique with the barrier heights being 0.6–0.7 eV for both n‐ and p‐type AlGaAsSb. The reason for the surface Fermi‐level pinning for Au and Al could be related to a predominance of Ga‐antisite–type native acceptors at the surface, which is not the case for Sb. Sulfur treatment of the surface is shown to decrease the barrier height for Au and to increase greatly the photosensitivity of Au Schottky diodes. The same effect is observed after treatment in a hydrogen plasma. In the latter case, changes in the Schottky barrier height are correlated with passivation of native acceptors in the bulk of the Al0.5Ga0.5As0.05Sb0.95.

Ohmic contacts of Au and Ag to p-GaSb

Abstract Evaporated contacts of Au, Au(Zn), Au(In, Zn) Au(Ge), Ag, Ag(Zn), Ag(Ge), Ag(Sn), Ag(In), In, In(Zn), In(Ge), and Al have been studied for p-GaSb(100) doped in the range 8 × 1016–1 × 1019 cm−3. Annealing was typically at a temperature 250–350°C for 10–30 min. A transmission line and other methods were used to determine the specific contact resistivity. For material of a carrier doping density 1018 cm−3 the contacts exhibited values about 5 × 10−5 Ω cm2. For other dopings the contact resistivity tended to be inversely proportional to the doping density, and at 1 × 1019 cm−3 the value was 5 × 10−6 Ω cm2. Ag contacts were stable in resistance for at least 100 h at 350°C and therefore may be expected to have little change over many thousands of hours at 70°C. The Au based contacts however began to increase in resistance after 30 h at 250°C. Models for the calculation of specific contact resistivity have been applied to p-GaSb and comparison with experimental results made.

The influence of hydrogen plasma treatment and proton implantation on the electrical properties of InAs

The effects produced in InAs by hydrogen plasma treatment and proton implantation are discussed. It is shown that both treatments can produce an n‐type layer at the surface of p‐InAs. For the hydrogen plasma treatment the effect is explained by hydrogen donors complexing with the Be and Zn acceptors and rendering them electrically inactive, thus leaving the residual donors uncompensated. In proton implanted samples the p‐n conversion is due to a creation of donor‐type lattice defects.

High‐resistivity GaSb grown by molecular‐beam epitaxy

GaSb undoped layers grown by molecular‐beam epitaxy on GaSb or on semi‐insulating GaAs substrates at temperatures between 600 and 630 °C are shown to have carrier concentrations in the low 1013 cm−3 range, corresponding to almost intrinsic conditions. The materials have been characterized using current‐voltage, capacitance‐voltage, Hall effect, photoluminescence, thermally stimulated current, and secondary‐ion mass spectrometry. Bulk GaSb (n type) is also found to have converted to high‐resistance p type after a heat treatment at 630 °C. Speculations are offered for the responsible mechanism, but a definitive explanation does not exist at this time.

The Effect of Hydrogen Treatment on Electrical Properties of AIGaAsSb

The effect of hydrogen treatment at 200°C on the concentration of electrically active defects in LPE grown AIGaAsSb is reported. In n-type layers the electrical properties are shown to be dominated by DX-like deep donors of three different types all of which are strongly passivated by the hydrogen treatment as evidenced by C-V. DLTS C-T and spreading resistance measurements. In p-type layers intrinsic acceptors of defect origin are also passivated by hydrogen. Deuterium profiles in both n- and p-type layers show characteristic plateaus indicative of formation of neutral compexes between hydrogen and dopants. Hydrogen treatment also leads to decrease of the Au/n-AIGaAsSb Schottky barrier height from 1.3 to 0.85 eV.

High Resistivity GaSb and GaAs Produced by MBE Growth at Elevated Temperatures

In this paper we show that when grown by MBE at unusually high temperatures epitaxial layers of GaSb and GaAs are semi-insulating. In GaSb combination of Hall effect, TSC, SIMS and two probe resistivity profiling leads us to believe that high resistivity is due to production of midgap centers at elevated temperatures. No strong evidence of the prevalence of such midgap centers was obtained for high temperature GaAs layers and in this case we believe that high resistivity is associated with the formation of Ga-related precipitates acting as internal Schottky barriers.