Hiroaki Matsumura

High-Power and Long-Lifetime InGaN Multi-Quantum-Well Laser Diodes Grown on Low-Dislocation-Density GaN Substrates

Epitaxially laterally overgrown GaN on free-standing GaN was used to reduce the threading dislocations which were widely scattered over the entire surface. The threading dislocation density of the GaN layer above the window area surrounding the SiO2 mask was reduced to 5×107/cm2, and that of the GaN layer above the SiO2 mask area was reduced to 7×105/cm2. InGaN multi-quantum-well laser diodes (LDs) grown on low-dislocation-density GaN substrates were demonstrated. LDs with an output power of 30 mW exhibited an estimated lifetime of 15,000 h at a case temperature of 60°C. At a case temperature of 25°C, the current at the output power of 30 mW and at the lasing threshold current were 42 mA and 23 mA, respectively. For comparison, LDs were grown on different substrates, and the dependence of their characteristics on the substrates was examined.

Room-Temperature CW Lasing of a GaN-Based Vertical-Cavity Surface-Emitting Laser by Current Injection

We report the demonstration of CW lasing at room temperature in a GaN-based vertical-cavity surface-emitting laser (VCSEL) by current injection. The active region of the VCSEL consisted of a two-pair InGaN/GaN quantum well active layer. The optical cavity consisted of a 7-λ-thick GaN semiconductor layer and an indium tin oxide layer for p-contact embedded between two SiO2/Nb2O5 dielectric distributed Bragg reflectors. The VCSEL was mounted on a Si substrate by wafer bonding and the sapphire substrate was removed by laser lift-off. Under CW operation for an 8-µm aperture device, the threshold current was 7.0 mA and the emission wavelength was approximately 414 nm.

Demonstration of Blue and Green GaN-Based Vertical-Cavity Surface-Emitting Lasers by Current Injection at Room Temperature

We realized room-temperature lasing of blue and green GaN-based vertical-cavity surface-emitting lasers (VCSELs), for the first time, by current injection. The blue GaN-based VCSEL had a threshold current of 1.5 mA and a threshold voltage of 3.3 V under continuous-wave operation. Its maximum output power was 0.70 mW and its laser emission wavelength was 451 nm. The green GaN-based VCSEL had a threshold current of 22 mA and a threshold voltage of 6.3 V under pulsed current operation. Its maximum output power was estimated to be over 0.80 mW and the laser emission wavelength was 503 nm.

Improvement in Lasing Characteristics of GaN-based Vertical-Cavity Surface-Emitting Lasers Fabricated Using a GaN Substrate

We compared the lasing characteristics of GaN-based vertical-cavity surface-emitting lasers (VCSELs) fabricated using a GaN substrate with those fabricated using a sapphire substrate. The original substrates are removed from the devices after the devices have been bonded to Si substrates. Consequently, with the exception of the cavity length, the two kinds of fabricated VCSELs have almost the same structures. The VCSELs fabricated using a GaN substrate have a higher maximum output power (0.62 mW) and longer lifetimes than those fabricated using a sapphire substrate. Even for the VCSELs fabricated with a GaN substrate, 10-min operation causes their threshold current to increase.

High-power and wide wavelength range GaN-based laser diodes

Since the first demonstration of a pulsed InGaN laser diodes (LDs) grown on sapphire substrate in 1995, we have been developing longer lifetime and higher optical output power LDs in the 400 - 410 nm wavelength range. Moreover, we have already succeeded in the expansion of the lasing wavelength range from ultraviolet (UV) to blue-green. In this paper, we reported the recent progress of high-power and wide wavelength range GaN-based LDs with an optical output power of 20 mW single mode (375nm), 160 mW single mode (405nm), 200 mW multi mode (405nm), 50 mW single mode (445nm), 300 mW multi mode (445nm), and 20 mW single mode (473nm).

GaN‐Based Light‐Emitting Diodes and Laser Diodes, and Their Recent Progress

It is recognized that GaN-based semiconductor is the most excellent material for short wavelength emitting devices. In this paper, we review the development of InGaN light emitting diodes (LEDs) and laser diodes (LDs). Additionally, purely-blue LDs are demonstrated, and the emission-wavelength dependence of the threshold current density is studied.