M. Hagerott Crawford

HIGH TEMPERATURE ELECTRON CYCLOTRON RESONANCE ETCHING OF GAN, INN, AND ALN

Electron cyclotron resonance etch rates for GaN, InN, and AlN are reported as a function of temperature for Cl2/H2/CH4/Ar and Cl2/H2/Ar plasmas. Using Cl2/H2/CH4/Ar plasma chemistry, GaN etch rates remain relatively constant from 30 to 125 °C and then increase to a maximum of 2340 A/min at 170 °C. The InN etch rate decreases monotonically from 30 to 150 °C and then rapidly increases to a maximum of 2300 A/min at 170 °C. This is the highest etch rate reported for this material. The AlN etch rate decreases throughout the temperature range studied with a maximum of 960 A/min at 30 °C. When CH4 is removed from the plasma chemistry, the GaN and InN etch rates are slightly lower, with less dramatic changes with temperature. The surface composition of the III–V nitrides remains unchanged after exposure to the Cl2/H2/CH4/Ar plasma over the temperatures studied.

Morphology and photoluminescence improvements from high-temperature rapid thermal annealing of GaN

Rapid thermal annealing of GaN in an Ar or N2 ambient up to 1100 °C is shown to improve surface morphology and photoluminescence intensity. For both ambients the average rms surface roughness as determined by atomic force microscopy decreases from ∼4 nm on the as‐grown material to ∼1 nm after a 1100 °C anneal. The band‐edge luminescence intensity was increased by a factor of 4 after a 1100 °C anneal in a N2 ambient and a factor of 2 for annealing at 1100 °C in an Ar ambient as compared to as‐grown material. The 1100 °C anneal improves the ratio of band edge to deep‐level luminescence and also reduces the electron concentration and mobility. The reduction in mobility can be explained in terms of a two‐band conduction mechanism where defect band conduction dominates at the lower carrier densities or an increase in the free‐carrier compensation ratio.

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.

Threshold investigation of oxide-confined vertical-cavity laser diodes

We report an experimental and theoretical analysis of the threshold properties of infrared oxide‐confined vertical‐cavity surface emitting lasers. We find good agreement between experiment and theory on the wavelength dependencies of the threshold current density and intrinsic voltage. The threshold voltage is shown to equal the sum of the calculated quasi‐Fermi energy separation and the ohmic drop arising from a record low 17 to 30 Ω series resistance in these vertical‐cavity lasers. Our analysis provides two independent means for determining the material threshold gain. A threshold gain of 500 cm−1 is found for these oxide‐confined lasers, which is half that estimated for ion‐implanted lasers with inferior electrical and optical confinement.

Improved AlGaInP‐based red (670–690 nm) surface‐emitting lasers with novel C‐doped short‐cavity epitaxial design

A modified epitaxial design leads to straightforward implementation of short (1λ) optical cavities and the use of C as the sole p‐type dopant in AlGaInP/AlGaAs red vertical‐cavity surface‐emitting lasers (VCSELs). Red VCSELs fabricated into simple etched air posts operate continuous wave at room temperature at wavelengths between 670 and 690 nm, with a peak output power as high as 2.4 mW at 690 nm, threshold voltage of 2.2 V, and peak wallplug efficiency of 9%. These values are all significant improvements over previous results achieved in the same geometry with an extended optical cavity epitaxial design. The improved performance is due primarily to reduced optical losses and improved current constriction and dopant stability.

EPITAXIAL DESIGN AND PERFORMANCE OF AlGaInP RED (650–690 nm) VCSELs

Progress in addressing critical epitaxial design issues associated with AlGaInP-based visible (red) vertical-cavity surface-emitting laser (VCSEL) diodes is reviewed, with emphasis on those issues that differentiate red VCSELs from conventional AlGaAs-based near-IR VCSELs. Key issues include epitaxial growth techniques for red VCSELs, the unique properties of AlGaInP alloys and heterostructures, design and growth of visible distributed Bragg reflectors, and integration of AlGaInP and AlGaAs hetero-structures into the hybrid VCSEL device structure. The performance characteristics of AlGaInP/AlGaAs red VCSEL diodes are overviewed in the context of the epitaxial design.

Transient photoinduced absorption in (AlxGa1−x)0.5In0.5P fractal quantum well heterostructures

Picosecond photoinduced absorption measurements have been performed on four different (AlxGa1−x)0.5In0.5P fractal quantum well heterostructures. The results of these measurements reveal that, at early times following pulsed excitation, the carriers remain near the surface layer in which they were photogenerated, and populate the higher lying branches of the V‐shaped fractal structure. With increasing time, the carrier population relaxes toward the lowest energy, central wall. The rate at which the relaxation occurs is governed by the characteristic layer of widths of the fractal structure.