Susumu Koike

GaN blue light emitting diodes prepared by metalorganic chemical vapor deposition

The epitaxial layers of GaN have been grown on (0001)‐oriented sapphire substrates using metalorganic chemical vapor deposition. The layers with good quality and relatively smooth surface morphology were obtained by enforcing growth in H2 after adherence of nuclei to the substrates in N2 atmosphere. Using this technique, GaN light emitting diodes with metal‐insulating n‐type structure were fabricated. Two kinds of blue electroluminescence were observed at room temperature with exciting voltage of 4–8 V with emission wavelength of 430 and 488 nm. The external efficiency is about 0.005%.

Study of cracking mechanism in GaN/α‐Al2O3 structure

Imperfection (cracking, stress) in (0001)GaN/(0001)α‐Al2O3 grown by using the metalorganic chemical vapor deposition (MOCVD) or chemical vapor deposition (CVD) method is investigated. First, the epitaxial relation is confirmed by using the oscillating‐crystal method. Subsequently, imperfections, especially cracks, are observed in detail by optical microscopy and x‐ray diffraction topography. Cracking occurs at the layer thickness larger than 13 μm in the crystals having epitaxial layers of good quality, while it does not appear even at the thickness of 30 μm in crystals including inferior layers. Finally, stress in the layer and in the substrate are determined by measuring the warp of the wafer. Compressive stress in the good epitaxial layer is 1.6×109 dyne cm−2, and in this case, cracking occurs at the maximum tensile stress in the substrate less than 3×108 dyne cm−2. However, cracking does not occur even at the compressive stress of 3×109 dyne cm−2 in the inferior layer and at the tensile stress of 1×10...

High efficient GaAlAs light‐emitting diodes of 660 nm with a double heterostructure on a GaAlAs substrate

A new type GaAlAs light‐emitting diode of 660 nm with a double heterostructure fabricated on a GaAlAs substrate has been developed. It can provide high efficiency of 8.0% and high speed response with a cut‐off frequency of 20 MHz. The GaAlAs substrate is transparent at the emission wavelength of 650–660 nm, bringing about a reduction of internal absorption to increase the efficiency. The DH structure produces a high speed of response by confining carriers in the thin active layer.

Very low threshold planar buried heterostructure InGaAsP/InP laser diodes prepared by three‐stage metalorganic chemical vapor deposition

Low threshold InGaAsP/InP lasers with planar buried heterostructure were grown entirely by low‐pressure metalorganic chemical vapor deposition (MOCVD). The threshold current Ith=10 mA and the differential quantum efficiency ηd =60%, which are comparable to lasers grown by liquid phase epitaxy, were obtained. Most lasers randomly selected from one wafer have threshold currents of Ith=10–25 mA, because of high thickness uniformity of MOCVD growth. Stable fundamental transverse mode operation was also obtained up to an output power of 40 mW/facet, due to controlling the active layer width less than 2 μm.

Crystallographic Characterization of ZnSxSe1-x Epitaxial Films

Crystalline quality of ZnSxSe1-x films grown on GaAs substrates has been investigated in detail using the X-ray double-crystal method. Respective fluctuations in orientation and spacing of lattice planes are measured separately. It is shown that the crystalline quality of ZnSxSe1-x films is noticeably affected by the fluctuation in orientation caused by lattice mismatch and partly by the fluctuation in spacing which may be associated with an inhomogeneous distribution of Se and S atoms. Improvement of the quality by lattice matching is due to a reduction of fluctuation in orientation.

InGaAsP multiple quantum well lasers with planar buried heterostructure prepared by metalorganic chemical vapor deposition

Planar buried heterostructure InGaAsP multiple quantum well (MQW) lasers consisting of six InGaAsP (λg =1.34 μm at room temperature) wells and five InP barriers were prepared by low‐pressure metalorganic chemical vapor deposition. The threshold current was 35 mA, and the differential quantum efficiency was 45% at an emission wavelength of 1.3 μm. In the temperature range from −35 to 30 °C, the characteristic temperature was T0=57 K. No significant improvement in T0 was observed in these MQW lasers. However, stable single longitudinal mode operation could be obtained in a wide range of injection current without any mode changes. This effect was considered to be a result of gain narrowing of the MQW lasers.

High‐efficiency GaP pure green light‐emitting diodes of 555 nm fabricated by new liquid phase epitaxy method

A new liquid phase epitaxy (LPE) method, which can control impurity concentration by volatilization of impurities from the growth solution under reduced pressure, has been developed. Using this LPE method, high‐efficiency GaP pure green light‐emitting diodes, of which the peak wavelength is 555 nm, has been obtained. The average efficiency for a epoxy‐encapsulated diode is 0.1% and the maximum efficiency is 0.14% at 16 A/cm2.

Metalorganic chemical vapor deposition of InGaAsP/InP layers and fabrication of 1.3‐μm planar buried heterostructure lasers

High‐quality InGaAsP and InP layers were obtained with good surface morphology by low‐pressure metalorgainic chemical vapor deposition (MOCVD). The growth apparatus could be relatively simple using trimethylindium (TMI) as indium source. Abrupt heterointerfaces were also obtained and the compositional grading at the interfaces was estimated to be less than 20–30 A owing to the low‐pressure growth technique. The selective burying growth on several types of mesas was investigated. The growth rate on the {111}B face was found to be smaller than that on the {111}A and the {100} face in MOCVD. As a result, very smooth and flat varying layers were obtained when the rectangular mesas were formed along the 〈110〉 direction. Using these characteristics, low‐threshold 1.3‐μm InGaAsP/InP lasers with planar buried heterostructures (PBH) were grown entirely by three‐stage MOCVD. The threshold current Ith =10 mA and the differential quantum efficiency ηd =60%, which are comparable to lasers grown by liquid‐phase epitaxy...

Strains in ZnSxSe1–x films grown on (001)-GaAs substrates

Abstract Strains in heteroepitaxial semiconductor film of ZnSe and ZnSxSe1-x grown on (001)-GaAs substrates have been investigated by using the 2θ/θ mode of the X-ray diffraction method. Firstly, a method of strain measurement is explored. In the ZnSe films, strains parallel to the interface are expansive for growth temperatures (TG) above 300°C, while compressive below this temperature. It is found that thermal and misfit strains contribute to the residual strains, and the former is dominant for TG>300°C, whereas the latter for TG>300°C. In the ZnSxSe1-x films grown at 450°C, the parallel strains are expansive and the magnitude varies with increasing fraction x. It is also found that coherent growth occurs at x=0.05 which corresponds to the misfit of 1.3×10-3 at TG=450°C.

A New Technique for Low Concentration Diffusion of Boron into Silicon

A new technique is proposed for doped-oxide diffusion of boron into silicon, providing a controlled surface concentration in a wide range from 1015 to 1020 cm-3. The principle is based on our finding that if the source borosilicate film deposited is heat-treated in an NH3 ambient prior to the drive-in step, the transfer of boron into silicon is remarkably suppressed. The concentration of boron diffused in silicon is strongly dependent on the temperature and/or time of the NH3-heat-treatment. It is also found that an undoped SiO2 or Si3N4 film deposited on the source film works as a mask against the NH3 ambient. As a result, a simultaneous local diffusion of boron can be performed from a single film source to plural regions where different boron profiles are desired.