F. A. Khan

Plasma-induced damage study for n-GaN using inductively coupled plasma reactive ion etching

In this article, we report a comprehensive study on plasma-induced damage for n-GaN using inductively coupled plasma (ICP) reactive ion etching. Effect of ICP coil power, etch duration and bias voltage on the electrical characteristics of n-GaN was investigated. It was observed that variation in ICP coil power and etch duration had minimal effect on varying the plasma-induced surface damage. Bias voltage was found to be the most significant cause of variation in plasma-induced damage to the surface of n-GaN. Therefore, low surface damage can be achieved by optimizing the bias voltage at which the sample is being etched. Auger electron spectroscopy analysis showed that the stoichiometry of the etched GaN surfaces was identical, independent of the etching conditions.

Thermal stability of rhenium Schottky contacts on n-type AlxGa1−xN

The impact of rapid thermal annealing on the electrical and materials characteristics of Re Schottky contacts on n-type GaN and AlxGa1−xN (x=0.10 and 0.26) was investigated. Effective barrier heights were obtained from current–voltage and modified Norde measurements on diodes annealed at up to 800 °C. For AlxGa1−xN with x>0, Schottky barrier heights were found to increase upon annealing from the as-deposited state, but decreased sharply after annealing at 600 °C. Modified Norde measurements indicate that this degradation could be explained by the existence of a shunt conduction path with an associated barrier height below 0.46 V, possibly a consequence of an inhomogeneous interface after annealing at temperatures above 600 °C. A new defect lying at 0.34 eV below the conduction band edge was also detected by deep level transient spectroscopy after contact degradation.

Inductively coupled plasma reactive ion etching of AlxGa1−xN for application in laser facet formation

The etching characteristics of AlxGa1−xN grown by metal–organic chemical-vapor deposition were investigated in an inductively coupled plasma (ICP) reactive ion etching system using Cl2/Ar gas mixtures. Etch rate variations with substrate bias voltage, ICP coil power, chamber pressure, Cl2/Ar gas mixture ratios, and gas flow rates were investigated. The optimum chamber pressure for etching was found to be dependent on both the substrate bias voltage and ICP coil power. Auger electron spectroscopy analysis showed that the stoichiometries of the etched Al0.22Ga0.78N surfaces were identical, independent of the etching conditions. Etching results were successfully applied to form highly anisotropic and smooth facets in GaN/InGaN/AlGaN heterostructure laser materials.

Low-Damage Etching of Silicon Carbide in Cl2-Based Plasmas

Fluorine-based plasmas have been extensively reported for etching SiC in inductively coupled plasma reactive ion etching (ICP-RIE) systems for device fabrication and via-hole formation. The primary advantage of fluorine-based plasmas for etching SiC is that they yield very high etch rates. However, while high etch rates are very suitable for via-hole formation into SiC, lower etch rates are desirable for SiC device fabrication. The etching of SiC using ICP-RIE in various Cl 2 -based mixtures is reported. It was found that in comparison with F 2 -based gas mixtures, Cl 2 -based gas mixtures induced less damage on etched SiC surfaces. Optimized etching conditions using BCl 3 /SF 6 gas mixtures that induce minimal surface damage on SiC are reported. Results of Auger electron spectroscopy showed that etching conditions produced negligible change in surface stoichiometry.

Ion-beam processing effects on the thermal conductivity of n-GaN/sapphire (0001)

We have measured high spatial/depth resolution (2–3 μm) thermal conductivity (κ) at 300 K before and after plasma-induced effects on two series of n-GaN sapphire (0001) samples fabricated by hydride vapor phase epitaxy using scanning thermal microscopy. The sample thicknesses were 50±5 μm for one set and 25±5 μm for the second. The carrier concentrations were ∼8×1016 cm−3 and ∼1.5×1017 cm−3, respectively, as determined by Hall effect measurements. The thermal conductivity before treatment was similar to that previously reported for hydride vapor phase epitaxy material with comparable carrier concentration and thickness [D. I. Florescu et al., J. Appl. Phys. 88, 3295 (2000)]. Damage was induced by ion-beam processing the samples under constant Ar+ gas flow and pressure for a fixed period of time (5 min), with the dc bias voltage (Vdc) being the only variable processing parameter (125–500 V). The thermal conductivity near the surface, κ, was found to exhibit a linear decrease with Vdc in the investigated ra...

Characteristics of Ti/Pt/Au ohmic contacts on p-type GaN/Al{sub x}Ga{sub 1-x}N superlattices

Ti/Pt/Au metallization on p-type GaN/Al{sub x}Ga{sub 1{minus}x}N (x = 0.10 and 0.20) superlattices (SL) were investigated as ohmic contacts. Current-voltage and specific contact resistance measurements indicate enhanced p-type doping in the superlattice structures compared to that in GaN. Ti/Pt/Au is shown to be an effective ohmic metallization scheme on p-type GaN/Al{sub x}Ga{sub 1{minus}x}N superlattices. A specific contact resistance of R{sub c} = 4.6 x 10{sup {minus}4} {Omega}-cm{sup 2} is achieved for unalloyed Ti/Pt/Au on GaN/Al{sub 0.2}Ga{sub 0.8}N Sl. This is reduced to 1.3 x 10{sup {minus}4} {Omega}-cm{sup 2} after annealing for 5 minutes at 300 C.

Dry and Wet Etching for Group III – Nitrides

The group-III nitrides have become versatile semiconductors for short wavelength emitters, high temperature microwave transistors, photodetectors, and field emission tips. The processing of these materials is significant due to the unusually high bond energies that they possess. The dry and wet etching methods developed for these materials over the last few years are reviewed. High etch rates and highly anisotropic profiles obtained by inductively-coupled-plasma reactive ion etching are presented. Photoenhanced wet etching provides an alternative path to obtaining high etch rates without ion-induced damage. This method is shown to be suitable for device fabrication as well as for the estimation of dislocation densities in n-GaN. This has the potential of developing into a method for rapid evaluation of materials.