Keisuke Yamane

High-quality {20-21} GaN layers on patterned sapphire substrate with wide-terrace

A {20-21} GaN layer was grown from a c-plane-like sapphire sidewall of a {22-43} patterned sapphire substrate according to the epitaxial relationship between c-GaN and c-sapphire despite {20-21} GaN is not growing on {22-43} sapphire. The as-grown {20-21} GaN layer had an m- and {10-11} facet structure. To improve the {20-21} GaN layer, a wide-terrace was attempted. The defects in the GaN layer were clustered on the m-facets, resulting in a dislocation density of less than 5.6 × 105/cm2 on the {10-11} facets. The {20-21} GaN layer had an excellent photoluminescence spectrum indicating a small number of defects.

Reduction in Dislocation Density of Semipolar GaN Layers on Patterned Sapphire Substrates by Hydride Vapor Phase Epitaxy

This paper presents the growth of thick semipolar {1011}, {1122}, and {2021} GaN layers on n, r, and {2243} patterned sapphire substrates (PSSs), respectively, by hydride vapor phase epitaxy. The reduction rate of the dislocation density varied with growth planes. For {1011} GaN layers, the dislocation density drastically decreased at over 100 µm, which was as fast the reduction rate as in the case of the c-plane. It was revealed that the reduction rate of the dislocation density could be controlled by the proper selection of the growth plane. Finally, we fabricated 2 in. freestanding semipolar GaN substrates via self-separation.

Operation of Monolithically-Integrated Digital Circuits with Light Emitting Diodes Fabricated in Lattice-Matched Si/III–V–N/Si Heterostructure

This report presents the successful operation of a 1-bit counter circuit with an optical output as a demonstration of monolithic optoelectronic integrated circuits. The circuit was fabricated in a lattice-matched Si/III–V–N/Si heterostructure, using p-type metal oxide semiconductor field effect transistors and light emitting diodes (LEDs). The generation of structural defects was significantly suppressed and smooth surfaces were formed. The carrier concentration of the Si-capping layer was decreased to (0.8–1.2)×1017 cm-3 by increasing the growth temperature. In the resulting chips, the red light emission from the LEDs was in synchronization with the logical values of input and output voltages.

Performance of InGaN/GaN light-emitting diodes grown using NH3 with oxygen-containing impurities

The performance of InGaN/GaN light-emitting diodes (LEDs) fabricated using NH3 was varied by intentionally adding H2O, O2, or CO. The oxygen concentration in the active layer varied with the type of impurity, which was related to the binding energy of the impurity. When a small amount of oxygen was incorporated in the InGaN active layer without Si doping through an oxygen-containing impurity, the light output power of the LED was improved. On the other hand, the light output power of the LED gradually deteriorated with increasing oxygen concentration. The oxygen-containing impurities affected the light output power of the LEDs. When NH3 with any oxygen-containing impurities was purified using a purification system giving a guaranteed impurity concentration of less than 10 ppb, the light output power of the LED was recovered to that of the LED fabricated with pure NH3.

Structural and optical properties of Eu-doped GaN nanocolumns on (111) Si substrates grown by RF-plasma-assisted molecular beam epitaxy

Eu-doped GaN (GaN:Eu) shows a sharp line emission and the thermal stability of the emission wavelength. To improve their optical properties, GaN:Eu nanocolumns were grown on GaN nanocolumn platforms with high crystalline quality by RF-plasma-assisted molecular beam epitaxy. The GaN:Eu growth temperature strongly affected the nancolumn configuration. Although a high growth temperature of more than 700 °C enhanced lateral growth, a low growth temperature of 600 °C led to independent GaN:Eu nanocolumns. Although it was revealed that an increase in Eu concentration brought about polycrystalline growth, the optically active site concentration increased with increasing Eu concentration without concentration quenching, which suggests that the nanocolumn crystal is a valuable material for developing the novel optical devices utilizing GaN:Eu.

Characterization of structural defects in semipolar GaN layers grown on patterned sapphire substrates

We present the transmission electron microscopy characterization of GaN layers grown by metal–organic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) on patterned sapphire substrates (PSSs). We determined that the predominant I1-type basal stacking faults (BSFs) propagated toward the surface without an annihilation reaction, even when the layer thickness was increased by HVPE, whereas some threading dislocations were annihilated through their coalescence. It is revealed that BSFs were generated owing to the growth on the −c plane facet at the initial stage of MOVPE growth. One way to improve the crystalline quality is to use PSSs with wide terraces to expand the defect-free region.

Origin of lattice bowing of freestanding GaN substrates grown by hydride vapor phase epitaxy

This paper describes a mechanism to explain the lattice bowing of freestanding GaN substrates grown by hydride vapor phase epitaxy on sapphire substrates. The freestanding GaN substrates typically exhibit a concave shape. It is revealed that the radius of curvature and lattice constant of the top surface are almost the same as those of the bottom surface. This is indicative of the complete relaxation of the GaN lattice, even though the freestanding GaN substrate exhibited a curvature. It is shown that dislocations are present in a plane normal to the growth direction in addition to conventionally known threading dislocations; these are referred to as in-plane dislocations. Based on these results, it is proven quantitatively that the extra-half planes related to the in-plane dislocations are primarily responsible for the phenomenon of lattice bowing.

Evaluation of {112̄2} Semipolar Multiple Quantum Wells Using Relaxed Thick InGaN Layers with Various In Compositions

We have succeeded in the growth of a high-quality semipolar {112} GaN layer on an r-plane patterned sapphire substrate (r-PSS). In this study, we fabricated light-emitting diodes (LEDs) using relaxed thick InGaN layers with various In compositions. There were significant changes in polarization properties, indicating lattice mismatch reduction due to the use of a relaxed thick InGaN layer. Electroluminescence (EL) intensity was improved by using a relaxed thick InGaN layer with low In composition. In particular, the EL intensity improved approximately twofold compared with that in the case of LEDs without relaxed thick InGaN layers at an injection current of 200 mA.

Self-Separation of Large Freestanding Semipolar {11bar 22} GaN Films Using r-Plane Patterned Sapphire Substrates

We have studied the growth of semipolar GaN from the etched sapphire sidewall of a patterned sapphire substrate (PSS). In this work, we grew a thick {112} GaN layer on an r-plane PSS (r-PSS) by hydride vapor phase epitaxy (HVPE) and separated the GaN layer from the r-PSS. We demonstrated the self-separation of the {112} GaN layer from the r-PSS by using a PSS and thick GaN growth. The ease of separation of the GaN layer from the PSS depended on the selective growth area of the sapphire sidewall. Consequently, we obtained a freestanding {112} GaN film of 2-in. diameter. The dark spot density of this film was 2.8×107/cm2.

Positional dependence of defect distribution in semipolar hydride vapor phase epitaxy-GaN films grown on patterned sapphire substrates

We have investigated the position dependence of crystalline quality and defect distribution in a semipolar hydride vapor phase epitaxy (HVPE)-GaN film grown on a patterned sapphire substrate (PSS). Position-dependent X-ray microdiffraction (XRMD) measurement clearly revealed the periodic fluctuation of the lattice plane tilting in HVPE-GaN films. This correlated with the periodic distribution of (a + c)-type dislocations owing to the patterning pitch of the PSS as confirmed by transmission electron microscopy (TEM). In the three-dimensional reciprocal lattice space map, the diffuse streak exactly along the c-axis can be clearly detected, indicating the presence of basal plane stacking faults in HVPE-GaN films. Furthermore, we have quantitatively estimated the defect densities from the results of XRMD and TEM measurements. From the obtained results of XRMD and TEM measurements, the fluctuation of the lattice plane tilting and the defect distribution in HVPE-GaN films grown on two types of metalorganic vapor phase epitaxy-GaN templates will be discussed in detail.