C. B. Vartuli

Ion implantation doping and isolation of GaN

N‐ and p‐type regions have been produced in GaN using Si+ and Mg+/P+ implantation, respectively, and subsequent annealing at ∼1100 °C. Carrier activation percentages of 93% for Si and 62% for Mg were obtained for implant doses of 5×1014 cm−2 of each element. Conversely, highly resistive regions (≳5×109 Ω/⧠) can be produced in initially n‐ or p‐ type GaN by N+ implantation and subsequent annealing at ∼750 °C. The activation energy of the deep states controlling the resistivity of these implant‐isolated materials is in the range 0.8–0.9 eV. These process modules are applicable to the fabrication of a variety of different GaN‐based electronic and photonic devices.

Wet chemical etching survey of III-nitrides

Abstract Wet chemical etching of GaN, InN, AlN, InAlN and InGaN was investigated in various acid and base solutions at temperatures up to 75°C. Only KOH-based solutions were found to etch AlN and InAlN. No enchants were found for the other nitrides, emphasizing their extreme lack of chemical reactivity. The native oxide on most of the nitrides could be removed in potassium tetraborate at 75°C, or HCl H 2 O at 25°C.

ICl/Ar electron cyclotron resonance plasma etching of III–V nitrides

Electron cyclotron resonance plasma etch rates for GaN, InN, InAlN, AlN, and InGaN were measured for a new plasma chemistry, ICl/Ar. The effects of gas chemistry, microwave and rf power on the etch rates for these materials were examined. InN proved to be the most sensitive to the plasma composition and ion density. The GaN, InN, and InGaN etch rates reached ∼13 000, 11 500, and ∼7000 A/min, respectively, at 250 W rf (−275 V dc) and 1000 W microwave power. The etched surface of GaN was found to be smooth, with no significant preferential loss of N from the surface at low rf powers, and no significant residue on the surface after etching.

CL2/AR AND CH4/H2/AR DRY ETCHING OF III-V NITRIDES

Electron‐cyclotron‐resonance (ECR) and reactive ion etching (RIE) rates for GaN, AlN, InN, and InGaN were measured using the same reactor and plasma parameters in Cl2/Ar or CH4/H2/Ar plasmas. The etch rates of all four materials were found to be significantly faster for ECR relative to RIE conditions in both chemistries, indicating that a high ion density is an important factor in the etch. The ion density under ECR conditions is ∼3×1011 cm−3 as measured by microwave interferometry, compared to ∼2×109 cm−3 for RIE conditions, and optical emission intensities are at least an order of magnitude higher in the ECR discharges. It appears that the nitride etch rates are largely determined by the initial bond breaking that must precede etch product formation, since the etch products are as volatile as those of conventional III–V materials such as GaAs, but the etch rates are typically a factor of about 5 lower for the nitrides. Cl2/Ar plasmas were found to etch GaN, InN, and InGaN faster than CH4/H2/Ar under ECR...

High temperature surface degradation of III–V nitrides

The surface stoichiometry, surface morphology, and electrical conductivity of AlN, GaN, InN, InGaN, and InAlN were examined at rapid thermal annealing temperatures up to 1150 °C. The sheet resistance of the AlN dropped steadily with annealing, but the surface showed signs of roughening only above 1000 °C. Auger electron spectroscopy (AES) analysis showed little change in the surface stoichiometry even at 1150 °C. GaN root mean square (rms) surface roughness showed an overall improvement with annealing, but the surface became pitted at 1000 °C, at which point the sheet resistance also dropped by several orders of magnitude, and AES confirmed a loss of N from the surface. The InN surface had roughened considerably even at 650 °C, and scanning electron microscopy showed significant degradation. In contrast to the binary nitrides, the sheet resistance of InAlN was found to increase by ∼102 from the as grown value (3.2×10−3 Ω cm) after annealing at 800 °C and then remain constant up to 1000 °C, while that of I...

Ion implantation and rapid thermal processing of III–V nitrides

Ion implantation doping and isolation coupled with rapid thermal annealing has played a critical role in the realization of high performance photonic and electronic devices in all mature semiconductor material systems. This is also expected to be the case for the binary III-V nitrides (InN, GaN, and A1N) and their alloys as the epitaxial material quality improves and more advanced device structures are fabricated. In this article, we review the recent developments in implant doping and isolation along with rapid thermal annealing of GaN and the In-containing ternary alloys InGaN and InAlN. In particular, the successful n- and p-type doping of GaN by ion implantation of Si and Mg+P, respectively, and subsequent high temperature rapid thermal anneals in excess of 1000°C is reviewed. In the area of implant isolation, N-implantation has been shown to compensate both n- and p-type GaN, N-, and O-implantation effectively compensates InAlN, and InGaN shows limited compensation with either N- or F-implantation. The effects of rapid thermal annealing on unimplanted material are also presented.

Implantation and redistribution of dopants and isolation species in GaN and related compounds

Twelve different elements used for doping or isolation were implanted into GaN (and selected species into AlN and InN), and the resulting range parameters were measured by secondary ion mass spectrometry. For lighter elements such as Be, F and H, the agreement between experimental range and range straggle determined using a Pearson IV computer fitting routine and those predicted by TRIM 92 calculations was good, but for heavier elements such as Ge and Se, the discrepancy can be as much as a factor of two in range. There was little redistribution of any of the investigated species up to 700°C, except for 2H in AlN and S in GaN. Elements such as F and Be, which are generally rapid diffusers in III–V compounds, do not display any redistribution in GaN for temperatures up to 800°C.

Temperature dependent electron cyclotron resonance etching of InP, GaP, and GaAs

Electron cyclotron resonance etching of InP, GaP, and GaAs in Ar, Ar/Cl 2, Ar/Cl2/H2, and Ar/Cl2/H2/CH4 plasmas is reported for substrate temperatures from 10 to 170 °C. Etch rates increased as a function of temperature for GaP and GaAs in an Ar/Cl2 plasma. With the addition of H2 or H2/CH4 to the plasma, the GaP and GaAs etch rates decreased and were essentially temperature independent. In comparison, InP etch rates showed a strong temperature dependence regardless of plasma chemistry. At 170 °C, InP etch rates were greater than GaP and GaAs in the Ar/Cl2/H2 and Ar/Cl2/H 2/CH4 plasmas. Atomic force microscopy was used to determine the root‐mean‐square roughness of the etched surfaces. The etched surface morphology for InP was strongly dependent on temperature and plasma chemistry while smooth pattern transfer was obtained for a wide range of plasma conditions for GaAs and GaP.

Nitrogen and fluorine ion implantation in InxGa1−xN

Implantation of N+ ions in n‐type InxGa1−xN (0.37≤x≤1.0) produces maximum increases in sheet resistance of 50–100 times upon annealing in the range of 400–600 °C. The dominant deep state introduced by implantation and annealing have ionization energies of ∼0.35–0.39 eV and therefore are relatively high in the band gap of the InGaN. There was no evidence for chemical deep levels associated with the implanted N+ or F+. The implant isolation behavior of n‐type InGaN appears analogous to that of InP and InGaAs.

Comparison of inductively coupled plasma Cl2 and Cl4/H2 etching of III-nitrides

A parametric study of etch rates, selectivity, surface morphology and etch anisotropy has been performed for Cl2 and CH4/H2 inductively coupled plasma (ICP) patterning of GaN, AlN, InN, InAlN, and InGaN at low dc self-biases (typically ⩽−100 V). Controlled etch rates in the range 500–1500 A min−1 are obtained for all materials. Surface morphology is a strong function of ion energy and plasma composition in both chemistries, while vertical sidewalls are obtained over a wide range of conditions because of the ion-driven nature of the etch mechanism.