Benjamin A. Haskell

Defect reduction in (11¯00) m-plane gallium nitride via lateral epitaxial overgrowth by hydride vapor phase epitaxy

This letter reports on extended defect density reduction in m-plane (11¯00) GaN films achieved via lateral epitaxial overgrowth (LEO) by hydride vapor phase epitaxy. Several dielectric mask patterns were used to produce 10 to 100 μm-thick, partially and fully coalesced nonpolar GaN films. X-ray rocking curves indicated the films were free of wing tilt. Transmission electron microscopy showed that basal plane stacking fault (SF) and threading dislocation (TD) densities decreased from 105cm−1 and 109cm−2, respectively, less than 3×103cm−1 and ∼5×106cm−2, respectively, in the Ga-face (0001) wing of the LEO films. SFs persisted in ⟨0001⟩-oriented stripe LEO films, though TD reduction was observed in the windows and wings. Band-edge cathodoluminescence intensity increased 2 to 5 times in the wings compared to the windows depending on the stripe orientation. SFs in the low TD density wings of ⟨0001⟩-stripe films did not appear to act as nonradiative recombination centers.

Demonstration of a semipolar (101¯3¯) InGaN∕GaN green light emitting diode

We demonstrate the growth and fabrication of a semipolar (101¯3¯) InGaN∕GaN green (∼525nm) light emitting diode (LED). The fabricated devices demonstrated a low turn-on voltage of 3.2V and a series resistance of 14.3Ω. Electroluminescence measurements on the semipolar LED yielded a reduced blueshifting of the peak emission wavelength with increasing drive current, compared to a reference commercial c-plane LED. On-wafer measurements yielded an approximately linear increase in output power with drive current, with measured values of 19.3 and 264μW at drive currents of 20 and 250mA, respectively. The external quantum efficiency did not decrease appreciably at high currents. Polarization anisotropy was also observed in the electroluminescence from the semipolar green LED, with the strongest emission intensity parallel to the [12¯10] direction. A polarization ratio of 0.32 was obtained at a drive current of 20mA.

Characterization of Planar Semipolar Gallium Nitride Films on Spinel Substrates

Specular, planar semipolar gallium nitride films were grown by hydride vapor phase epitaxy. Planar films of (1013) and (1122) GaN have been grown on (1010) m-plane sapphire. The in-plane epitaxial relationship for (1013) GaN was [3032]GaN ∥[1210]sapphire and [1210]GaN ∥[0001]sapphire. The in-plane epitaxial relationship for (1122) GaN was [1121]GaN ∥[0001]sapphire and [1100]GaN ∥[1210]sapphire. The (1013) films were determined to have N-face sense polarity and a threading dislocation density of 9×108 cm-2. The (1122) films have Ga-face sense polarity and have a threading dislocation density of 2×1010 cm-2. The basal plane stacking fault density was 2 ×105 cm-1 for both orientations. The RMS roughness of the films was under 10 nm for a 5 ×5 µm2 area.

Demonstration of nonpolar m-plane InGaN/GaN light-emitting diodes on free-standing m-plane GaN substrates

We report the fabrication of nonpolar m-plane InGaN/GaN multiple-quantum well light-emitting diodes (LEDs) on free-standing m-plane GaN substrates. On-wafer continuous wave output power of 240 µW was measured at 20 mA for a 300×300 µm2 device, and output power as high as 2.95 mW was measured at 300 mA. There was no sign of saturation of the output power at high drive currents. An emission peak at 450 nm was obtained on electroluminescence measurements with high drive currents. The current-voltage characteristics of these LEDs showed rectifying behavior with a turn-on voltage of 3–4 V.

Structural and morphological characteristics of planar (112̄0) a-plane gallium nitride grown by hydride vapor phase epitaxy

This letter discusses the structural and morphological characteristics of planar, nonpolar (1120) a-plane GaN films grown on (1102) r-plane sapphire by hydride vapor phase epitaxy. Specular films with thicknesses over 50 μm were grown, eliminating the severely faceted surfaces that have previously been observed for hydride vapor phase epitaxy-grown a-plane films. Internal cracks and crack healing, similar to that in c-plane GaN films, were observed. Atomic force microscopy revealed nanometer-scale pitting and steps on the film surfaces, with rms roughness of ∼2 nm. X-ray diffraction confirmed the films are solely a-plane oriented with on-axis (1120) and 30° off-axis (1010) rocking curve peak widths of 1040 and 3000 arcsec, respectively. Transmission electron microscopy revealed a typical basal plane stacking fault density of 4×105 cm−1. The dislocation content of the films consisted of predominately edge component (bedge=±[0001]) threading dislocations with a density of 2×1010 cm−2, and mixed-characte...

Limiting factors of room-temperature nonradiative photoluminescence lifetime in polar and nonpolar GaN studied by time-resolved photoluminescence and slow positron annihilation techniques

Room-temperature nonradiative lifetime (τnr) of the near-band-edge excitonic photoluminescence (PL) peak in {0001} polar, (112¯0), (11¯00), and (001) nonpolar GaN was shown to increase with the decrease in density or size of Ga vacancies (VGa) and with the decrease in gross density of point defects including complexes, leading to the increase in the PL intensity. As the edge threading dislocation density decreased, density or size of VGa tended to decrease and τnr tended to increase. However, there existed remarkable exceptions. The results indicate that nonradiative recombination process is governed not by single point defects, but by certain defects introduced with the incorporation of VGa, such as VGa-defect complexes.

Milliwatt Power Blue InGaN/GaN Light-Emitting Diodes on Semipolar GaN Templates

Growth of semipolar Group-III nitrides based devices offers a means of reducing the deleterious effects of the polarization-induced electric fields present in the polar quantum wells. We report on the fabrication of blue InGaN/GaN multiple-quantum well light-emitting diodes (LEDs) on semipolar (10-1-1) and (10-1-3) oriented GaN templates. A maximum on-wafer continuous wave output power of 190 µW was measured at 20 mA for 300×300 µm2 devices, and output power as high as 1.53 mW was measured at 250 mA. Drive-current independent electroluminescence peak at 439 nm was observed for the LEDs grown on both the planes. The current–voltage characteristics of these LEDs showed rectifying behavior with a forward voltage of 3–4 V at 20 mA.

Prospective emission efficiency and in-plane light polarization of nonpolar m-plane inxGa1-xN/GaN blue light emitting diodes fabricated on freestanding GaN substrates

Prospective equivalent internal quantum efficiency (ηint) of approximately 34% at 300K was demonstrated for the blue emission peak of nonpolar m-plane (11¯00) InxGa1−xN∕GaN multiple quantum well light emitting diodes (LEDs) fabricated on freestanding m-plane GaN substrates. Although the ηint value is yet lower than that of conventional c-plane blue LEDs (>70%), the results encourage one to realize high performance green, amber, and red LEDs by reducing the concentration of nonradiative defects, according to the absence of the quantum-confined Stark effects due to the polarization fields parallel to the quantum well normal. The electric field component of the blue surface emission was polarized perpendicular to the c axis with the in-plane polarization ratio of 0.58 at 300K.

Properties of nonpolar a-plane InGaN/GaN multiple quantum wells grown on lateral epitaxially overgrown a-plane GaN

The properties of nonpolar a-plane InGaN∕GaN multiple-quantum wells (MQWs), grown simultaneously on lateral epitaxially overgrown (LEO) a-plane GaN and planar a-plane GaN, were studied. High-resolution x-ray diffraction analysis revealed that the In mol fraction in the MQWs grown on LEO-GaN was significantly lower than that on planar a-plane GaN. The lower In incorporation was confirmed by microphotoluminescence (μ-PL) and wide-area photoluminescence measurements, which showed a redshift of the MQW emission from 413 nm for the nearly defect-free laterally overgrown regions to 453 nm for the defective “window” regions of the LEO a-plane GaN, to 478 nm for the high-defect density planar a-plane GaN. μ-PL measurements also demonstrated that the emission from the nearly defect-free wings of the LEO a-plane GaN was more than ten times stronger than the emission from the defective windows.

Nonpolar m-Plane Blue-Light-Emitting Diode Lamps with Output Power of 23.5 mW under Pulsed Operation

We report on the DC and pulsed performance of nonpolar m-plane InGaN/GaN multiple-quantum-well light-emitting diode (LED) lamps. LED structures were grown on free-standing m-plane GaN substrates by metalorganic chemical vapor deposition. LEDs with an area of 300×300 µm2 were packaged into conventional epoxy-encapsulated lamps. The emission wavelength of the LEDs was 452 nm. A CW output power as high as 0.6 mW was achieved at a drive current of 20 mA, corresponding to an external quantum efficiency of 1.09%. Pulsed power measurement on the lamps yielded an output power of 23.5 mW at a drive current of 1 A for a duty cycle of 0.25%.