Shiro Yamasaki

EFFECTS OF SURFACE TREATMENTS AND METAL WORK FUNCTIONS ON ELECTRICAL PROPERTIES AT P-GAN/METAL INTERFACES

In order to examine the possibility of preparing a nonreacted (nonalloyed) Ohmic contact to p-GaN, the effects of GaN surface treatments and work functions of the contact metals on the electrical properties between the metal contacts and p-GaN were investigated. A contamination layer consisting of GaOx and adsorbed carbons was found on the GaN substrate grown by metalorganic chemical vapor deposition. The contamination layer was not completely removed by sputtering the GaN surface with Ar and N ions where the ion densities were ∼10−2 μA/cm2. Although the contamination layer was partially removed by immersing in a buffered HF solution, little improvement of the electrical properties of the GaN/metal interfaces was obtained. Most of the contamination layer was removed by annealing the Ni and Ta contacts at temperatures close to 500 °C. These annealed contacts exhibited slightly enhanced current injection from the contact metal to the GaN. The present surface treatment study indicated that removal of the con...

Schottky barriers and contact resistances on p‐type GaN

We measured the Schottky barrier heights and specific contact resistivities of four different metals on p‐type GaN. The Schottky barrier heights of Pt, Ni, Au, and Ti were obtained from the current‐voltage characteristics to be 0.50, 0.50, 0.57, and 0.65 eV, respectively. The specific contact resistivities were 0.013, 0.015, 0.026, and 0.035 Ω⋅cm2, respectively. Our experimental results proved that the Schottky barrier heights and specific contact resistivities decrease with increase in metal work function as expected theoretically.

p‐type conduction in Mg‐doped Ga0.91In0.09N grown by metalorganic vapor‐phase epitaxy

p‐type conduction in InN‐containing nitrides doped with Mg has been achieved by metalorganic vapor‐phase epitaxy. The hole concentration at room temperature is as high as 7×1017 cm−3. The activation energy of a Mg acceptor is estimated to be 204 meV. D–A pair emission with peak wavelength of about 405 nm is enhanced by thermal annealing.

HIGH-QUALITY GAINN/GAN MULTIPLE QUANTUM WELLS

High‐quality Ga0.92In0.08N–GaN multiple quantum wells structures (MQW) were grown successfully by metalorganic vapor phase epitaxy. Fine multilayer structures with a thickness period of 7–9 nm were detected by secondary ion mass spectroscopy. The dislocation density in the MQW was found to be in the range of 0.5–2×109 cm−2 by transmission electron microscopy. The MQW extremely enhanced by two orders of magnitude, the cathodoluminescence intensity compared with bulk Ga0.91In0.09N.

GaN/GaInN/GaN double heterostructure light emitting diode fabricated using plasma-assisted molecular beam epitaxy

High-quality GaN and Ga1-x Inx N (x≤0.2) have been grown by RF-plasma-assisted molecular beam epitaxy (RF-MBE) on the GaN/AlN/sapphire substrate grown by metalorganic vapor-phase epitaxy for the first time. GaN and GaInN showed intense near-band-edge photoluminescence (PL) at room temperature. A double hetero-structure (DH) of p-GaN:Mg/Ga0.8In0.2N/ n-GaN has been fabricated. The DH light emitting diode showed intense violet emission upon current injection at room temperature.

Dependence of electrical properties on work functions of metals contacting to p-type GaN

Abstract The effects of GaN surface treatments and work functions of the contact metals on the electrical properties at the p-GaN/metal interfaces were investigated. A contamination layer consisting of GaO x and adsorbed carbons was found on the GaN substrate grown by metalorganic chemical vapor deposition. Most of the contamination layer was removed by annealing the Ni and Ta contacts at temperatures close to 500°C, resulting in slight increase of the current injection from the contact metal to the GaN. The resistance at the p-GaN/metal interfaces decreased exponentially with increasing the metal work functions, indicating that the Schottky barrier heights were sensitive to the metal work functions. The present study concluded that the contact metal with the large work function should be chosen to obtain for the non-reacted (non-alloyed) ohmic contacts to the p-GaN. However, non-reacted ohmic contacts to the p-GaN did not provide the low contact resistance required for blue laser diodes.

GaInN/GaN multiple quantum wells green LEDs

The high-efficient blue, green light-emitting diodes (LEDs) using GaInN/GaN multiple quantum wells (MQW) have been successfully developed. The peak wavelength of MQW blue and green LEDs are approximately 460nm and 520nm, respectively. The full width at half-maximum of the MQW blue LEDs is 40nm at a forward current of 20mA which is much narrower than 70nm of the conventional blue LEDs. The degrees of shift in peak wavelength of the MQW blue and green LEDs are less than 5nm in the current ranging from 5mA to 50mA.

GaN-based MQW light-emitting devices

The GaN-based MQW laser diodes have been improved excellently by introducing GaN/GaInN optical-guiding. The continuous wave laser operation at room temperature has been achieved at the wavelength of 410 nm. The lifetime of room temperature continuous wave operation is longer than 60 minutes at around 1 mW output. The external efficiencies of GaInN/GaN MQW blue and green light emitting diodes (LEDs) have been increased by newly developed flip-chip (FC) type LED lamp structure. The luminous intensities of the FC-type blue and green LEDs were typically 6 cd and 14 cd at 20 mA, respectively. The FC-type blue and green LEDs are the brightest levels in the world currently. The peak wavelengths and full widths at half maximums were typically 464 nm and 27 nm for the blue LEDs, and 515 nm and 32 nm for the green LEDs.

Room Temperature CW Operation of GaN-Based Blue Laser Diodes by GaInN/GaN Optical Guiding Layers

GaN-based short wavelength laser diodes are the most promising key device for a digital versatile disk. We have been improving the important points of the laser diodes in terms of optical guiding layers, mirror facets. The continuous wave laser irradiation at room temperature could be achieved successfully by reducing the threshold current to 60 mA (4 kA/cm 2 ). We have tried to apply the multi low temperature buffer layers to the laser diodes for the first time to reduce the crystal defects.

GaN-based multiple quantum well light-emitting devices

The GaN-based multiple quantum wells (MQW) laser diodes have been improved excellently by introducing GaN/GaInN optical- guiding layers and by reducing dislocation density. The lifetime of continuous wave operation has been improved to longer than 300 hours with 3 mW at the wavelength of 409 nm.