Koshi Tamamura

Carbon incorporation in metalorganic chemical vapor deposition (Al,Ga)As films grown on (100), (311)A, and (311)B oriented GaAs substrates

The amount of carbon in GaAs and (Al,Ga)As films depends on the orientation of crystals grown by metalorganic chemical vapor deposition. We investigated the relation between the incorporation of carbon and the orientation of crystals using (100), (311)A, and (311)B substrates. The concentration of electrons on (311)B substrates of unintentionally doped films was higher than those of the films on (100) and (311)A substrates. The films grown on (311)B substrates did not show p‐type behavior even when they were grown with a fairly low V/III ratio. The relative intensity of the free‐to‐carbon acceptor luminescence of the films grown on (311)B substrates was smaller than that of films grown on the other substrates. This is consistent with the results of carbon contamination indicated by secondary ion mass spectra. Furthermore, a reduced peak in photoluminescence caused by defects was observed when (311)B substrates were used.

Effective speckle reduction in laser projection displays

Two alternative methods for effectively reducing the speckle noise in laser based rear and front projection displays are studied and demonstrated. Firstly, widening of the laser emission spectrum to nearly 4nm by tailoring the structures of 640nm band AlGaInP/GaInP based edge emitting broad-area red laser diode arrays, realized a reduction of speckle contrast from 20% to an acceptable level of 5%. Designing the power/wavelength distribution of the multiple emitters to achieve a flat top profile for the total spectrum plays an important role in maximizing the speckle reduction effect. This approach could easily be adapted to laser diodes arrays of other materials or wavelengths. Secondly, relative oscillation movement within the screen layers can also reduce the speckle contrast to the acceptable level of 5%. The moving layer material and the oscillation period has been studied and optimized to maximize the reduction level for both rear and front projection configurations. The two speckle reduction techniques were evaluated on a front projector utilizing a red laser assisted UHP lamp hybrid light source, and showed significant enhancement in view ability by the suppression of speckle. Combining the two techniques lead to further reduction in speckle and scintillation noise to a supreme level of 2%, enabling a practical solution for wide color gamut and high efficiency laser projection displays.

AlGaAs/GaAs distributed feedback laser diodes grown by MOCVD

Abstract AlGaAs/GaAs distributed feedback (DFB) laser diodes emitting at 880 and 760 nm were fabricated by a two-step MOCVD growth technique. Epitaxial growth was carried out in a conventional atmospheric-pressure MOCVD system with a vertical reactor. A mesa-stripe geometry and separate-confinement heterostructure (SCH) was employed for the laser structure. The cladding layer ( x = 0.35, 0.48) was successfully regrown on the guiding layer ( x = 0.15, 0.25) corrugated with a 0.25 μm period (2nd order grating). Continuous wave (CW) operations were achieved up to 53°C for devices emitting at 880 nm and up to 10°C for devices emitting at 760 nm. A threshold current as low as 55 mA was obtained for a device emitting at 880 nm under CW operation at room temperature.

Magnesium doping of (Al,Ga)As in metalorganic chemical vapor deposition

Magnesium doping of AlxGa1−xAs in metalorganic chemical vapor deposition and the properties of the grown layer have been investigated. Bis‐cyclopentadienylmagnesium, CP2Mg, was used as a precursor of Mg. The hole concentration increased linearly from 3.5×1016 to 1×1019 cm−3 when the ratio of CP2Mg to trimethylgallium was increased. The carrier concentration increased with the increase of Al concentration, decreased with the increase of growth temperature, and was independent of the ratio of arsine to column III elements, V/III. The photoluminescence (PL) intensity increased when the growth temperature was increased and/or the V/III ratio was increased. The intensity of a deep PL band associated with near band‐edge emission, usually seen in the low‐temperature PL spectra of Zn‐doped (Al,Ga)As, was smaller than that in Zn‐doped (Al,Ga)As. The activation energy of the Mg acceptor deduced from the temperature dependence of the carrier concentration was smaller than that of the Zn acceptor.

545 nm Room-Temperature Continuous-Wave Operation of BeZnCdSe Quantum-Well Green Laser Diodes with Low Threshold Current Density

We report the growth of BeZnCdSe quantum-well laser diode (LD) structures with a short-period superlattice cladding layer and demonstrate continuous-wave lasing in the pure-green spectral region (545 nm) at room temperature. The threshold current density and voltage of a 5-?m-wide gain-guided laser were found to be 1.7 kA/cm2 and 10.4 V, respectively. This threshold current density is sufficiently low compared with that of InGaN/GaN green LDs.

Dislocation density of lattice mismatched epitaxial layers

Abstract Heteroepitaxial InAs, GaAs and Si layers were grown by vapor phase deposition. Having determined that the dislocation density of InAs layers on GaAs substrates is about 1×104 cm-2, that of Si on GaAs is less than 104 cm-2, and that of GaAs on InAs substrates is about 1×108 cm-2, we classified these growth systems into two categories, low and high dislocation density. We ascribed that the dislocation density was related to the formation of islands in the early stages of epitaxial growth.

Photoluminescence study on the interface of a GaAs/AlxGa1−xAs heterostructure grown by metalorganic chemical vapor deposition

The interface of a GaAs/AlxGa1−xAs heterostructure grown by metalorganic chemical vapor deposition has been studied by photoluminescence spectroscopy by using a step‐etching technique. Luminescence peaks associated with vacancy complexes emitted from both GaAs and AlxGa1−xAs layers were observed, and these peaks were remarkably intense on both sides of the GaAs/AlxGa1−xAs interface region. This result can be explained by the accumulation of vacancies in the interface region. The cause of this vacancy accumulation at the interface is discussed.

AlGaAs/GaAs distributed feedback lasers with first‐order grating fabricated by metalorganic chemical vapor deposition

Distributed feedback AlGaAs/GaAs lasers with first‐order grating (1295 A) were fabricated and successfully operated under continuous wave conditions at room temperature. A coupling coefficient of 115 cm−1 and a threshold current of 47 mA were obtained. A stable single‐mode oscillation was maintained up to 100 °C.

Coherent Si growth on GaAs substrates by vapor phase deposition

Epitaxial Si layers with low dislocation density were grown on GaAs substrates by pyrolysis using disilane. The dislocation density evaluated from SECCO etching (HF:H2 SO4 :K2 Cr2 O7 =100 cc:50 cc:2g) was less than 104/cm2, which is lower by two orders of magnitude than that of the GaAs layer on Si substrates. We found that the electron mobility of Si layers on GaAs substrates could be raised by decreasing the growth rate and a high mobility value the same as that of a homoepitaxial layer was obtained, although the Si layers were contaminated by an arsenic impurity of 1018 cm−3 .

540-nm green room-temperature CW operation of BeZnCdSe single quantum well laser diode

Room temperature continuous-wave operation at 540 nm was demonstrated with a BeZnCdSe quantum-well laser-diode. Threshold current density of the narrow stripe, 800 µm cavity laser was as low as ∼1.7 kA/cm²