Tsuyoshi Kotani

Composition dependence of the band gaps of In1−xGaxAs1−yPy quaternary solids lattice matched on InP substrates

The In‐Ga‐As‐P quaternary phase diagram required for the growth of lattice‐matched In1−xGaxAs1−yPy layers on InP substrates has been determined experimentally at 650 °C. The liquidus isotherms were obtained by the seed‐dissolution technique. The solidus iostherms were determined by electron‐microprobe analysis performed on surfaces of quaternary epitaxial layers grown on Sn‐doped InP (111) B substrates from quaternary saturated melts. Lattice constants of layers were measured by an x‐ray‐diffraction technique. The liquid‐phase‐epitaxy growth conditions of lattice‐matched In1−xGaxAs1−yPy (0⩽x⩽0.47, 0⩽y⩽1.0) layers on InP were found from the results of the phase diagram and lattice constant measurements. Lattice‐matched layers with various band gaps (from 1.34 to 0.74 eV at room temperature) were grown by using these conditions. Band gaps of the layers were determined by photoluminescence measurements at 300 and 77 K. The band gap at each temperature was found to be linearly dependent on alloy‐composition p...

Observation of etch pits produced in InP by new etchants

Abstract New etchants, HBr/HF or HBr/CH 3 COOH, produced sharp etch pits on (100) and (111) slices of InP. The etch pit shape produced on (100) by HBr/HF was pyramidal. The shape on (100) produced by HBr/CH 3 COOH varied from pyramidal to elongated rectangular along 〈110〉 with increasing the composition ratio of CH 3 COOH to HBr. The shape produced on (111)B by HBr/HF or HBr/CH 3 COOH was triangular pyramidal. The etch rates of these new etchants and HBr/H 3 PO 4 were measured as a function of composition ratio at room temperature. The correspondence between pits and dislocations was examined and the results indicated that etch pits produced by these etchants corresponded to dislocations.

High-efficiency long-lived GaAlAs LED's for fiber-optical communications

A new fiber-mounted GaAlAs LED has been proposed and developed to satisfy efficient performance and high-reliability requirements in Practical fiber-optical communication systems. By utilizing the lens effect of a spherical-ended fiber, the LED-to-fiber coupling is greatly improved and a coupling efficiency of 8.5 percent is obtained. At a forward current of 100 mA, the output power of 305 µW is obtained from 0.14-numerical-aperture 85- µm-core step-index fiber of 3-cm length. The power in the cladding part of the fiber is almost completely removed by the epoxy. Long-term operating-life tests of LEDs described here are in progress. After about 8000 h of operation, no power reduction has occurred. The accelerated aging at elevated temperatures has also been performed and an activation energy of 0.5 eV has been determined for DLD-free LEDs. A half-life in excess of 106h is estimated for room-temperature operation at a constant-current density of 10 kA/cm2.

Defect structure of degraded Ga1−xAlxAs double‐heterostructure light‐emitting diodes

The defect structure of degraded Ga1−xAlxAs double‐heterostructure (DH) light‐emitting diodes (LED’s) was investigated by electroluminescence (EL) topography and transmission electron microscopy (TEM). Two types of dark‐line defects (DLD’s), 〈100〉 DLD’s and 〈110〉 DLD’s, and dark‐spot defects (DSD’s) were observed in EL patterns of degraded LED’s. Dislocation dipoles or large zigzag‐shaped dislocation loops were associated with DSD’s and 〈100〉 DLD’s. The dipoles had Burgers vectors of the type (a/2) 〈011〉 inclined at 45° to the (001) junction plane or (a/2) 〈110〉 parallel to the junction plane and were extrinsic in character. The zigzag‐shaped dislocation loops had Burgers vectors of the type (a/2) 〈011〉 and were extrinsic in character. On the other hand, multiple stacking faults which lay in 〈110〉 directions or half dislocation loops which also lay in 〈110〉 directions and had Burgers vectors of the type (a/2) 〈011〉 inclined at 45° to the junction plane or (a/2) 〈110〉 parallel to the junction plane were as...

Nature of dark defects revealed in InGaAsP/InP double heterostructure light emitting diodes aged at room temperature

The nature of the dark defects which have appeared in the InGaAsP/InP double heterostructure light emitting diodes aged at room temperature were studied by transmission electron microscopy and other related methods. According to the observation of many diodes by electroluminescence topography, the dark defects were classified into five types: cross‐hatched 〈110〉 dark line defects, regular tetragonal 〈110〉 dark line defects, regularly distributed dark spot defects, dark band defects, and dark spot defects whose circumference was bright. These dark defects corresponded to misfit dislocations, stacking faults which originated from the interface between the epitaxial layer and the substrate, precipitate‐like spherical defects, mechanical damages induced during epitaxial growth, and alloyed regions produced by the penetration of the electrode metals, respectively. It was found that both the dislocation glide process and the dislocation climb motion due to the nonradiative recombination of the minority carriers...

Dependence of Ga1-xAlxAs LPE layer thickness on solution composition

The dependence of LPE growth thickness on the solution composition is examined in a Ga-Al-As system. A simple expression for the changing rate of As at the interface (dXLAs/dθ) is given and the calculated values of dXLAs/dθ are compared with experimentally obtained LPE layer thicknesses to show the linear relationship between these quantities; The growth process and As diffusivity in the Ga-Al-As system are discussed.

Defect structure of 〈100〉 dark lines in the active region of a rapidly degraded Ga1−xAlxAs LED

The 〈100〉 dark‐line defects (DLD’s) in the active region of a rapidly degraded Ga1−xAlxAs LED were observed by transmission electron microscopy (TEM). Dislocation networks, which contain dislocation dipoles and a number of dislocation loops, were associated with 〈100〉 DLD’s. The dipole extended in the 〈100〉 or 〈210〉 direction and was extrinsic in character; its Burgers vector was a/2 〈011〉 inclined at 45° to the junction plane. These results were very similar to those of GaAs‐Ga1−xAlxAs double‐heterostructure (DH) lasers.

Positive feedback model of defect formation in gradually degraded GaAlAs light emitting devices

Defects in gradually degraded GaAlAs (0.8 µm wavelength) light emitting diodes have been evaluated by transmission electron microscope (TEM) and deep-level transient spectroscopy (DLTS). Two stages increase of deep-level defects has been observed by DLTS during device operation (reported in a previous paper). On the other hand, very small dislocation loops (15-50 nm in diameter) were observed in the active region by TEM at the end of the device operation. The nature of the dislocation loops was determined to be interstitial Frank loops with Burgers vector of (a/3)

Mechanism of catastrophic degradation in 1.3‐μm V‐grooved substrate buried‐heterostructure lasers with the application of large pulsed currents

Catastrophic degradation of V‐grooved substrate buried‐heterostructure InGaAsP/InP lasers (λ=1.3 μm), by large pulsed currents, has been investigated using scanning electron microscopy, etching technique, energy dispersive x‐ray spectroscopy, and spatially resolved photoluminescence topography. After the degradation, the diode stops lasing and becomes ohmic. These are associated with the following phenomena: (i) facet erosion inside or outside the stripe region; (ii) penetration of the electrode‐metals into the epitaxial layer. These phenomena are presumably caused by the abrupt passage of large current along the facet or by local heating at the contact region outside the stripe region. Catastrophic optical damage, which frequently occurs in GaAlAs/GaAs double‐heterostructure lasers, is not observed in any part of the degraded diodes.

TEM Observation of Dark Defects Appearing in InGaAsP/InP Double-Heterostructure Light Emitting Diodes Aged at High Temperature

Dark defects which appear during high temperature aging of InGaAsP/InP 1.27 µm double-heterostructure light emitting diodes, were investigated by transmission electron microscopy and energy dispersive X-ray spectroscopy. Dark-spot defects are often observed in the electro-luminescent patterns of aged diodes, while cross-shaped dark-line defects are rarely observed. The dark-spot defects, which correspond to bar-shaped precipitates, are thought to be generated by the precipitation of the host atoms during operation at certain nucleation centers. The cross-shaped dark-line defects, which are associated with complicated defects consisting of small dislocation clouds and fibrous edge-like dislocations, are thought to be generated by local melting at In and/or P rich inclusions.