Masaaki Onomura

Room Temperature Pulsed Operation of Nitride Based Multi-Quantum-Well Laser Diodes with Cleaved Facets on Conventional C-Face Sapphire Substrates

We demonstrate room temperature pulsed operation of nitride based multi-quantum-well (MQW) laser diodes with cleaved mirror facets grown on a conventional C-face sapphire substrate. Cleavage was performed along the direction of the sapphire substrate, and the resultant facet was analyzed using an atomic force microscope (AFM) and theoretical calculation. A single peak emisson, at a wavelength of 417.5 nm, with a full width at half-maximum of 0.15 nm, was obtained. The threshold current density of the laser was 50 kA/cm2 and a voltage for the threshold current was 20 V.

THERMAL ANALYSIS FOR GAN LASER DIODES

Improvement in temperature characteristics of GaN laser diodes is important for realizing reliable devices operating at high temperatures. Thermal characteristics of GaN lasers have been analyzed by using a three-dimensional thermal conduction model. Maximum operation temperature has also been calculated. It was shown that the reduction in the stripe width as well as the reduction in threshold current density and operation voltage is very important for improving the temperature characteristics of GaN laser diodes.

Reactive Ion Beam Etching and Overgrowth Process in the Fabrication of InGaN Inner Stripe Laser Diodes

Dry etching and overgrowth process techniques have been developed for the fabrication of InGaN inner stripe laser diodes. The dry etch damage at the etched surface and the overgrown interface was estimated using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS). As a result, the etch damage at the overgrown interface was shown to be repaired during the overgrowth. Groove stripes formed on the GaN layer by reactive ion beam etching (RIBE) were overgrown by GaN using metalorganic chemical vapor deposition (MOCVD). The morphology of the overgrown surface was observed by scanning electron microscopy (SEM). The grooves of widths less than 10 µm were buried completely at 1100°C and smooth, flat surfaces were obtained. We have fabricated the InGaN inner stripe (IS) lasers and reported on the first pulsed lasing operation of InGaN inner stripe lasers, fabricated by dry etching and overgrowth techniques.

Analysis of Device Characteristics for InGaN Semiconductor Lasers

Carrier overflow and perpendicular transverse mode in InGaN multi-quantum-well lasers have been analyzed by numerical calculation. A high acceptor concentration for the p-type cladding layer and the reduction of the active layer volume have a large effect on the reduction of carrier overflow. Anti-guide-like behavior of the waveguide mode is formed in InGaN laser structures where the cladding layers have insufficient thickness. The layer structure should be designed so as to reduce the carrier overflow and suppress the anti-guide-like mode.

High-speed 1.5- mu m compressively strained multi-quantum well self-aligned constricted mesa DFB lasers

A great improvement in the high-speed characteristics for compressively strained multi-quantum-well (MQW) distributed-feedback (DFB) lasers with self-aligned constricted mesa structures is described. Negative wavelength detuning is an important factor in making possible the extraction of potential advantages for the compressively strained MQW DFB lasers. A 17-GHz bandwidth, which is the highest among the 1.5- mu m MQW DFB lasers, is demonstrated. A wavelength chirp width of 0.42 nm at 10 Gb/s is obtained due to a reduced linewidth enhancement factor that has a magnitude of less than 2. Nonlinear damping K factor in a DFB laser with 45-nm negative detuning has drastically decreased to 0.13 ns, about half of that for unstrained MQW lasers. This is mainly due to an enhanced differential gain as large as 6.9*10/sup -12/ m/sup 3//s. The estimated intrinsic maximum bandwidth is 68 GHz. >

Effect of metal type on the contacts to n-type and p-type GaN

Abstract The electrical properties of various metal contacts to both n-type and p-type GaN were investigated to determine the underlying trend between the metallic contact workfunction and the resultant Schottky barrier height between the said contact and the GaN material. It is concluded that, contrary to the expected trend, Fermi level pinning is not only present but is quite strong, with the effect being greater in the p-type material. The S factor (the index of interface behaviour) was seen to be reduced from 1.00 to 0.21 and 0.01 for n and p-type GaN, respectively.

Wavelength tuning mechanism in three-electrode DFB lasers

The wavelength tuning mechanism is investigated for three-electrode distributed feedback (DFB) InGaAs-InGaAsP lasers. It is shown that the side and center sections play different roles in wavelength tuning: the former determines the effective Bragg wavelength and the latter contributes through the round-trip phase condition. The lasing wavelength is expressed in a simple form that renders the wavelength shift behavior exceedingly understandable. The indispensability of the thermal contribution to continuous broad range tuning is also clarified both theoretically and experimentally.<<ETX>>

The Influence of Surface Treatment on the Quality of Pd/Au Contacts to p-type ZnSe.

The influence of surface treatment prior to the deposition of Pd/Au metallic contacts to p-type ZnSe is discussed. The methods studied being a sulphur based treatment and a CuSex contact treatment. The results show that both of these form better quality contacts, with lower applied voltages for set current densities, in comparison to an untreated sample. Although, the barrier height increased for the sulphur treated sample, by 0.11 eV to 0.69 eV, the active contact area was increased by an order of magnitude. The CuSex treatment is shown to reduce the Schottky barrier height to 0.50 eV but the active contact area was severely reduced in this case.

Electron Traps due to Defect-Impurity Complexes Induced by the Deformation of Epitaxial GaAs Grown on Si-Doped Substrate

Dependence of deformation induced deep levels on substrate impurities and deformation conditions was studied. Electron traps such as EB4 and EB6 were dominantly induced when undoped VPE GaAs grown on Si-doped substrates was deformed at temperatures higher than 600°C, whereas EL2, HL2(LPE-B) and Cu levels were dominant in deformed VPE layers on Cr-doped substrates. These results indicate that the deformation induced defects easily make complexes with impurities in the substrates, and that the EB4 and EB6 are not simple defects but are complexes with Si impurities.

Highly efficient InGaN MQW LEDs grown on 200 mm Si substrates

We demonstrate InGaN MQW LEDs on Si substrates have both high performance and low cost structure. The blue LED structures were grown by metal-organic chemical vapor deposition via unique buffer layers on 200 mm-diameter Si (111) substrates. The epitaxial wafers had slightly ex-situ convex bow without micro-cracks. Median and standard deviation of dominant wavelength by photoluminescence measurement were 448.9 nm and 2.0 nm within 4 mm edge exclusion, respectively. XRC FWHMs of GaN (0002) and GaN (10-12) were 341 arcsec and 388 arcsec, respectively, corresponding to be estimated to edge dislocation density of 2.0 × 109 /cm2. The blue LED structures were fabricated by legacy 8-inch (200-mm) Si device equipment without remodeling, because no particular thicker Si wafer was needed for our LED epitaxial growth. Encapsulated blue lamps were fabricated after dicing with 45 × 45 mil2. Median light output power of 641 mW was obtained under injection current of 350 mA at 25 deg-C. The operating voltage was 2.9 V. It corresponds to wall plug efficiency, WPE of 63 %. Stable operation more than 6,000 hours under 450 mA at 85 deg-C was confirmed. These results suggest the InGaN MQW LEDs on the large-scale Si wafers are promising for the near future solid-state lighting.