Chiaki Sasaoka

Room-Temperature Continuous-Wave Operation of InGaN Multi-Quantum-Well Laser Diodes Grown on an n-GaN Substrate with a Backside n-Contact

Continuous-wave operation at room-temperature has been demonstrated for InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on low-dislocation-density n-GaN substrates with a backside n-contact. The current, current density and voltage at the lasing threshold were 144 mA, 10.9 kA/cm2 and 10.5 V, respectively, for a 3 µm wide ridge-geometry diode with high-reflection dielectric coated mirrors. Single-transverse-mode emission was observed in the far-field pattern of the LDs and the beam full width at half power in the parallel and perpendicular directions was 6° and 25°, respectively.

High-quality InGaN MQW on low-dislocation-density GaN substrate grown by hydride vapor-phase epitaxy

Abstract A low-dislocation-density thick GaN layer was successfully grown using selective-area HVPE growth combined with epitaxial lateral overgrowth. The InGaN MQWs fabricated on this thick GaN layer showed superior optical properties compared with that on a sapphire substrate. Mg diffusion, induced by threading dislocations, was greatly suppressed for the LEDs on the HVPE-grown GaN layer. The results clearly indicate that the HVPE-grown GaN substrate will be useful for achieving high-performance light-emitting devices.

Novel Ridge-Type InGaN Multiple-Quantum-Well Laser Diodes Fabricated by Selective Area Re-Growth on n-GaN Substrates

A novel ridge structure fabricated by selective-area epitaxial re-growth is proposed for InGaN multiple-quantum-well (MQW) laser diodes (LDs). This technique is capable of precisely controlling the active ridge width and height, thus enabling stable single tran sverse-mode operation. Together with a backside n-contact on a low-dislocation-density GaN substrate, this structure provides high productivity and performance for GaN-based blue-violet LDs. A stable fundamental transverse mode up to 40 mW was demonstrated for the certain range of ridge dimensions. The minimum aspect ratio of the far-field patterns (FFPs) was about 2.1 in the fabricated ridge-type InGaN MQW LDs.

Aluminum selective area deposition on Si using diethylaluminumchloride

Aluminum deposition on Si was studied using diethylaluminumchloride (DEAlCl) as a new Al chemical vapor deposition source. Selective area deposition was successfully achieved at substrate temperatures of 313–380 °C. The deposition rate was higher than 370 A/min. Reflectance and resistivity of the deposited films were comparable to those of the evaporated ones. Decomposition experiments suggest that DEAlCl catalytically decomposes on the Al surface, which would explain the high selectivity observed.

Reflectance spectroscopy on GaN films under uniaxial stress

The uniaxial stress effects on valence band structures in GaN are investigated by reflectance spectroscopy. It is observed that the energy separation between A and B valence bands increases with the application of uniaxial stress in the c plane. The experimental results are analyzed on the basis of the k⋅p theory, and deformation potential D5 is determined as −3.3 eV. It is indicated that the uniaxial strain effect could be utilized for improving GaN-based laser performance.

Temperature programmed desorption study of GaAs(100)−c(4×4) and As4 exposed (2×4) surfaces

Abstract GaAs(100)−c(4×4) and As4 exposed (2×4) surfaces are studied using temperature programmed desorption (TPD) and reflection high energy electron diffraction (RHEED). The As sensitive factor for a quadrupole mass spectrometer is precisely calibrated and the As coverage is determined from As2 desorption spectra. For the c(4×4) surface, there are two steps in the As desorption process. Coverage analysis indicates that the c(4×4) structure is formed at an As coverage, θAs, of 1.28 monolayer (ML) and an additional As adsorption is possible up to a θAs of 1.61 ML without disturbing the reconstruction. At higher θAs, a repulsive interaction between adsorbed As dimers is suggested. On the As4 exposed (2×4) surfaces, the chemisorbed As desorbs at 430 and 500°C as As2. Based on RHEED observations, As2 peaking at 500°C is assigned to desorption due to transition from a (2×4)-γ to a (2×4) surface structure. The structures of these surfaces are discussed based on our TPD results and previously proposed structure models.

Anomalous As desorption from InAs(100) 2×4

Arsenic desorption from the InAs(100) 2×4 surface is investigated through temperature programmed desorption (TPD), isothermal desorption, and reflection high‐energy electron diffraction. TPD area analysis indicates that the As coverage, θAs, of the InAs 2×4 structure is 0.7 monolayers. The As TPD spectrum shows two desorption features; a broad tail from 300 to 400 °C and a distinct peak at 430 °C. The 430 °C peak is well described in terms of a first‐order‐desorption kinetics with a preexponential factor ν of 1.5×1019 s−1. This extremely high ν value explains well the narrow window of optimal molecular beam epitaxy growth conditions for InAs.

Atomic Layer Epitaxy of GaAs Using Solid Arsenic and DEGaCl

ALE growth of GaAs was reported using solid arsenic and DEGaCl. An abrupt shutoff of arsenic vapor was successfully achieved and monolayer growth was obtained independent of DEGaCl partial pressure. Grown surfaces were mirror-like at growth temperatures of 400~550°C. Grown layers showed p-type conductivity. The carrier concentration of the grown layers was rather low compared with that reported in DEGaCl-AsH3 ALE. QMS measurements of the DEGaCl decomposition rate suggest that DEGaCl completely decomposes to GaCl before reaching the substrate, which is considered to result in lower carbon contamination.

Study of Nitrogen Inhomogeneity in LPE GaP by Spatially Resolved Photoluminescence

Nitrogen inhomogeneity in LPE GaP is studied by spatially resolved photoluminescence. It is found that the nitrogen is doped much less under the macrostep riser which is composed of high-density atomic steps. The origin of this nonuniformity is discussed and it is concluded that the equilibrium concentration of nitrogen along a step is frozen in the bulk crystal, and hence the bulk concentration shows the step velocity dependence.

Theoretical study of the Cl desorption reaction induced by H2 in the chloride atomic layer epitaxy

Abstract The chloride ALE (atomic layer epitaxy) technique is now common to grow GaAs crystals, where the GaCl molecule is used to supply Ga atoms for the As dangling bond site. The present ab initio molecular orbital calculations predict that Cl atoms are desorbed as HCl by the single-site reaction which is induced by H 2 . The reaction scheme is represented as > GaCl + H 2 → > GaH + HCl , which is driven by the concerted electron delocalizations among those four atoms. It is shown that the reaction is endothermic by the amount of 30 kcal/mol and occurs through the four-centred transition state of “late-barrier” type. The activation energy is estimated to be 37–44 kcal/mol, which agrees well with the experimental value of 40–50 kcal/mol.