Takashi Jimbo

Improved Characteristics of Blue and Green InGaN-Based Light-Emitting Diodes on Si Grown by Metalorganic Chemical Vapor Deposition

We report significantly improved characteristics of InGaN multiple-quantum well blue and green light-emitting diodes (LEDs) on Si (111) substrates using metalorganic chemical vapor deposition. A high-temperature-grown thin AlN layer and AlN/GaN multilayers have been used for the growth of high-quality active layer on Si substrate. The blue LED on Si exhibited an operating voltage of 4.1 V, a series resistance of 30 Ω, an optical output power of 18 µW and a peak emission wavelength of 478 nm with a full width at half maximum of 22 nm at 20 mA drive current. These characteristics are comparable to those of LED on sapphire substrate. The green LED was also fabricated on Si substrate successfully.

Improved dc characteristics of AlGaN/GaN high-electron-mobility transistors on AlN/sapphire templates

High-electron-mobility transistors (HEMTs) have been demonstrated on both AlN/sapphire templates and sapphire substrates, and the dc characteristics of the fabricated devices were examined at room temperature. Better dc characteristics with high extrinsic transconductances and drain current densities were observed in the HEMTs grown on AlN/sapphire templates when compared with the HEMTs on sapphire substrates. Extrinsic transconductances of 214 and 137 mS/mm for Wg/Lg=15/2u2009μm HEMTs on AlN/sapphire templates and HEMTs on sapphire substrates were achieved, respectively. The enhancement of dc characteristics with small variations in threshold voltage (⩽130u2009mV) is due to the reduction of dislocation density (1.5×108u2009cm−2). The decrease of dark spot density has been confirmed in the GaN grown on AlN/sapphire templates using cathodoluminescence measurements. The advantage of using AlN/sapphire templates is that low dislocation density GaN layers at a high temperature can be grown without using low-temperature-g...

InGaN multiple-quantum-well green light-emitting diodes on Si grown by metalorganic chemical vapor deposition

We report the characteristics of InGaN multiple-quantum-well (MQW) green light-emitting diodes (LEDs) on Si (111) substrates. The MQW LEDs were grown on Si by metalorganic chemical vapor deposition using Al0.27Ga0.73N/AlN intermediate layers. The LED on Si showed an operating voltage of 7 V, a series resistance of 100 Ω, an optical output power of 20 μW, and a peak emission wavelength of 505 nm with a full width at half maximum of 33 nm at 20 mA drive current. The optical output power was half as compared to that of green LED on sapphire. The LED also exhibited a stable operation over 500 h under automatic current control (20 mA) condition at 27u200a°C.

Realization of GaAs/AlGaAs Lasers on Si Substrates Using Epitaxial Lateral Overgrowth by Metalorganic Chemical Vapor Deposition

In this paper, we report on the fabrication and characterizations of a GaAs-based laser using the epitaxial lateral overgrowth (ELO) technique. ELO is an epitaxial growth technique capable of yielding low-dislocation-density III-V films on Si. To realize the effectivity of this procedure, two types of lasers were fabricated by changing the positions of the top p+-GaAs and metal contact in-line with the ELO layer and in-line with the line seed region. The longer lifetime for the lasers with the top p+-GaAs and metal contact in-line with the ELO layer proves the suitability of the ELO technique.

Growth of high-quality GaN films on epitaxial AlN/sapphire templates by MOVPE

High-quality GaN films were grown on epitaxial AlN/sapphire templates by metal-organic vapor phase epitaxy. The Hall mobility as high as 790 cm2/V s with the carrier concentration of 7.6×1016 cm−3 at 300 K along with low dislocation density of 5×107 cm−2 have been achieved. The X-ray rocking curve full-width at half-maximum were 61 and 232 arcsec for the (0 0 0 4) and (2024) reflections, respectively. Atomic force microscopy images showed smooth surface morphology and clear step formation. Additionally, pit terminations could be hardly found. Photoluminescence measurement revealed a higher intensity near the band edge.

Anomalous compositional pulling effect in InGaN/GaN multiple quantum wells

A series of InGaN/GaN multiple quantum wells (MQWs) was grown by metalorganic chemical vapor deposition with different well thickness. High-resolution x-ray diffraction studies revealed that the In composition is increasing along the growth direction from the bottom to the top of each well layer in these MQWs. While the In composition at the bottom of each well layer almost keeps constant, the increasing rate of In composition becomes obviously larger when the growth temperature is decreased. The important conclusion of this study is that the InGaN/GaN MQWs is shaped like a triangle due to the increasing of In composition from the bottom to the top of the well layer. The emission mechanism of the InGaN/GaN MQWs has to be discussed based on the triangular band gap structure.

High-bright InGaN multiple-quantum-well blue light-emitting diodes on Si (111) using AlN/GaN multilayers with a thin AlN/AlGaN buffer layer

InGaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs) on Si (111) substrate were grown by metalorganic chemical vapor deposition. Crack-free films on 2-inch wafer were obtained using AlN/GaN multilayers with a thin AlN/AlGaN buffer layer. High-resolution X-ray diffraction (HRXRD) reveals the LED on Si is of high crystalline quality. Dislocation density of MQW active layer was investigated by cathodoluminescence (CL) at room temperature. The operating voltages of 3.7 V and 4.2 V and the output powers of 34.8 µW and 34.5 µW at 20 mA were obtained for the lateral and the vertical conduction, respectively. The forward series resistances are 33 Ω and 42 Ω for the lateral and the vertical conduction, respectively. The EL peaks at 453 nm with a full width at half maximum (FWHM) of 22 nm at 20 mA current. These characteristics are comparable to those of LED on sapphire. Especially, the LED on Si shows a high saturation operating current due to the good thermal conductivity of Si substrate.

Demonstration of an InGaN-based light-emitting diode on an AlN/sapphire template by metalorganic chemical vapor deposition

Structural, electrical, and optical properties of an InGaN-based light-emitting diode (LED) on an AlN/sapphire template have been studied and compared with the conventional LED properties on a sapphire substrate. In comparison to the LED on sapphire, the LED on AlN/sapphire template has shown better electrical and optical characteristics, which are due to a low threading dislocation density, high resistive, and thermal conductive AlN layer. An additional advantage is to grow a high-quality LED structure on an AlN/sapphire template without using low-temperature-grown GaN or an AlN buffer layer.

Suppression of crack generation in GaN/AlGaN distributed Bragg reflector on sapphire by the insertion of GaN/AlGaN superlattice grown by metal-organic chemical vapor deposition

GaN/AlGaN distributed Bragg reflectors (DBRs) have been grown on sapphire by metal-organic chemical vapor deposition. A GaN/AlGaN superlattice (SL) was introduced prior to the growth of the DBR to suppress crack generation. By introducing the SL, GaN layers in the DBR were highly compressed and the in-plane lattice constants were close to those of AlGaN layers in the DBR. For the 30 pairs of GaN/Al0.41Ga0.59N DBRs, the reflectivity was improved from 93% to 98% by the introduction of the 100 periods of GaN/AlGaN SL, and the generation of cracks was effectively suppressed.

Valence-Band Discontinuity at the AlN/Si Interface

The major problems of GaN-based light-emitting diodes on Si are their high series resistances and high operating voltages due to the large band discontinuity at the AlN/Si interface. We have observed the valence-band discontinuity at the AlN/Si interface using X-ray photoelectron spectroscopy (XPS). The valence- and conduction-band discontinuity values at the AlN/Si interface were found to be 2.8±0.4 eV and 2.3±0.4 eV, respectively.