Mathew C. Schmidt

High Power and High External Efficiency m-Plane InGaN Light Emitting Diodes

High power and high efficiency nonpolar m-plane (1100) nitride light emitting diodes (LEDs) have been fabricated on low extended defect bulk m-plane GaN substrates. The LEDs were grown by metal organic chemical vapor deposition (MOCVD) using conditions similar to that of c-plane device growth. The output power and external quantum efficiency (EQE) of the packaged 300 ×300 µm2 was 23.7 mW and 38.9%, respectively, at 20 mA. The peak wavelength was 407 nm and <1 nm redshift was observed with change in drive current from 1–20 mA. The EQE shows a minimal drop off at higher currents.

Demonstration of Nonpolar m-Plane InGaN/GaN Laser Diodes

The first nonpolar m-plane (1-100) nitride laser diodes (LDs) have been realized on low extended defect bulk m-plane GaN substrates. The LDs were grown by metal organic chemical vapor deposition (MOCVD) using conditions similar to that of c-plane device growth. Broad area lasers were fabricated and tested under pulsed conditions. Lasing was observed at duty cycles as high as 10%. These laser diodes had threshold current densities (Jth) as low as 7.5 kA/cm2. Stimulated emission was observed at 405.5 nm, with a spectral line-width of 1 nm.

Continuous-wave Operation of AlGaN-cladding-free Nonpolar m-Plane InGaN/GaN Laser Diodes

We demonstrate continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN laser diodes without Al-containing waveguide cladding layers. Thick InGaN quantum wells (QWs) are used to generate effective transverse optical mode confinement, eliminating the need for Al-containing waveguide cladding layers. Peak output powers of more than 25 mW are demonstrated with threshold current densities and voltages of 6.8 kA/cm2 and 5.6 V, respectively. The unpackaged and uncoated laser diodes operated under CW conditions for more than 15 h.

AlGaN-Cladding-Free Nonpolar InGaN/GaN Laser Diodes

We have previously demonstrated the AlGaN-cladding-free (ACF) laser diode (LD) concept over a wide visible spectral range and various nonpolar/semipolar crystallographic orientations. The benefits of this ACF epitaxial design include lower operating voltages and higher production yields. Nonpolar LDs have been demonstrated out to 500nm1 with semipolar reaching as long as 534nm2. No results have been published on nonpolar/semipolar orientations for short wavelength LDs. In this paper we report on the short wavelength limits of this epitaxial design on nonpolar bulk m-plane GaN substrates.

High-Efficiency Blue and True-Green-Emitting Laser Diodes Based on Non-c-Plane Oriented GaN Substrates

Using non-c-plane bulk GaN substrates, we demonstrate continuous-wave single-mode blue-emitting laser diodes operating with over 23% wall plug efficiency and over 750 mW output power, which represent the highest values reported to date. Furthermore, we demonstrate continuous-wave 520 nm green-emitting laser diodes with over 60 mW output power and 1.9% wall plug efficiency. The rapid performance evolution of laser diodes fabricated on non-c-plane orientations is validation of the benefits resulting from increased electron–hole overlap, reduced effective hole mass, and increased design flexibility.

Study of nonpolar m-plane InGaN∕GaN multiquantum well light emitting diodes grown by homoepitaxial metal-organic chemical vapor deposition

Nonpolar m-plane (11¯00) InGaN-based light emitting diodes (LEDs) grown on low-extended defect density bulk m-plane GaN substrates offer great potential for high performance devices due to the absence of polarization-related internal electric fields. To optimize the quantum well (QW) structure, systematic sets of near blue-ultraviolet LEDs using different well widths, barrier widths, and QW periods were packaged and tested. With increasing current, high power LEDs were realized with fairly flat external quantum efficiency and blueshift-free peak wavelength for QWs with thicknesses from 8to20nm, barrier widths from 10to22nm, and QW numbers from 4 to 10.

Electrical Characteristics of Nonpolar InGaN-Based Light-Emitting Diodes Evaluated at Low Temperature

The present article is a follow-up of our previous article [Jpn. J. Appl. Phys. 45 (2006) 7661]. InGaN-based light-emitting diodes of nonpolar orientation were grown on high-quality commercial GaN substrates. Results of low-temperature characterization showed that they were electrically conductive at temperature as low as 5 K. This experimental confirmation of electrical conduction at low temperature contradicts our previous results and the discussion of conduction mechanism returns to an impurity-concentration-related mechanism.

Epitaxial Lateral Overgrowth of High Al Composition AlGaN Alloys on Deep Grooved SiC Substrates

Fully coalesced Al0.93Ga0.07N films were demonstrated by metalorganic chemical vapor deposition on deep grooved SiC substrates. Lateral Al0.93Ga0.07N growth was achieved at low V/III ratios during growth. The deep grooves enabled coalescence despite of parasitic growth in the trenches. Dislocation reduction in the overgrown regions of the films was observed by transition electron microscopy and atomic force microscopy.

High-power high-efficiency continuous-wave InGaN laser diodes in the violet, blue, and green wavelength regimes

We present new advances in green, blue, and violet InGaN-based laser diodes fabricated on nonpolar and semipolar GaN substrates. Using these novel crystal orientations, we report high power, high efficiency, continuous-wave operation from single-lateral-mode electrically pumped laser diodes at wavelengths from 405 nm to 500 nm. Additionally, we present continuous-wave lasing demonstrations out to 523 nm, representing the longest continuous-wave green laser emission reported to date. Wall-plug efficiencies of over 25% in the violet region, 16.2% in the blue region, and 2.2% in the 500 nm range are presented. These InGaN-based devices offer dramatic improvement in size, weight, and cost over conventional gas or solid state lasers and may enable a variety of new applications in defense, biomedical, industrial, and consumer projection displays.

Smooth Top-Down Photoelectrochemical Etching of m-Plane GaN

Photoelectrochemical PEC etching of c-plane GaN has been studied extensively because it is one of only a few available damage-free wet-etching techniques for this material system. Because of its nonpolar nature and low defect density, m-plane GaN may benefit from PEC etching even more than c-plane GaN has. With m-plane GaN, it is possible to achieve smooth, controllable etching, bandgap-selective top-down etching, and deep, anisotropic etching. We have investigated PEC etching of m-plane GaN in KOH and HNO3 and have found etch rates ranging from less than 10 nm/min to more than 1 m/min, with roughness that is crystallographic in nature but small in scale. Etch selectivity of 60:1 between In0.1Ga0.9N and GaN is observed using PEC etching with filtered light. Anisotropic etching to depths as great as 75 m was achieved, with the sidewall profile of the etch controlled by the direction of incident light.