Masao Aiga

Uniform Fabrication of Highly Reliable, 50-60 mW-Class, 685 nm, Window-Mirror Lasers for Optical Data Storage

Uniform fabrication of highly reliable 50–60 mW-class 685 nm laser diodes (LDs) with a window-mirror structure has been realized by using selective solid-phase Zn diffusion and three-inch full wafer processing. A window-mirror structure at the LD mirror is formed by Zn-induced disordering of an ordered GaInP multiple quantum-well (MQW) active layer. High uniformity of characteristics such as the operating current and the far-field pattern has been obtained by realization of highly uniform Zn diffusion. A small astigmatic distance (ΔZ3 µ m), a low relative intensity noise (RIN-135 dB/Hz) and a high speed response (T r, T f1.2 ns) are obtained in addition to the high-power and high-temperature characteristics (70 mW, 80° C) in spite of the existence of the window structure. The LDs have exhibited reliable 6,000–10,000 h operation under the conditions of 60° C and 50–60 mW for the first time.

Metalorganic vapor-phase epitaxial regrowth of InP on reactive ion-etched mesa structures for p-substrate buried heterostructure laser application

Growth behavior of sulfur-doped n-InP around reactive ion-etched (RIE) mesas has been investigated for realization of p-substrate buried heterostructure laser utilizing metalorganic vapor phase epitaxy. It is found that the growth of n-InP layer on the sidewall of the mesa ((1 1 0) plane) is significantly suppressed, as the flow rate of hydrogen sulfide (H2S) which is used for n-type doping, increased. This phenomenon of growth suppression was also observed for growth of highly S-doped n-InP on narrow (0 0 1) facets. Taking account of both, these phenomena can be explained by migration enhancement of indium atoms on sulfur-terminated surfaces caused by excess H2S supply. Consequently, the shape of the regrown embedding layer was found to be exactly controlled by the H2S flow rate. Using this technique, a p-substrate 1.3 μm buried heterostructure laser with pnp current-blocking structure has been successfully fabricated around the RIE mesa and excellent lasing characteristics with high reliability has been realized for the first time.

Stability of amorphous silicon alloy triple‐junction solar cells and modules

Results on reliability test for amorphous silicon alloy triple‐junction solar cells and modules are described. It has been found that, for a‐SiGe:H pin cells, reduction of the stress in the film is of first importance for stability. Application of low‐temperature‐deposited microcrystalline p‐layer for each sub cell and of thinner i‐layers for the middle and the bottom cells improves stability of triple‐junction cells, by enhancing the electric field in the i‐layers.

High-resolution X-ray diffraction studies on growth interrupted heterointerfaces grown by metalorganic vapor-phase epitaxy

Abstract We have investigated the behavior of group V atoms at growth interrupted heterointerfaces in an InP/AsH 3 -exposure/InP multilayer structure grown by metalorganic vapor-phase epitaxy, whose interfaces are exposed to AsH 3 gases, by means of high-resolution X-ray diffraction on an atomic scale and its simulation technique. It is found that primary factors for the incorporation of arsenic (As) atoms into InP layers consists of two modes, one is the incorporation into the grown layer due to the substitution of phosphorus (P) atoms by As atoms, and the other is that into the subsequently grown InP layer due to the incorporation from solid deposition of As atoms on the susceptor. In the processes, P atoms are substituted by As atoms not only in the monolayer of the surface but also in the internal layer. It is also found that the depth where the As atoms are incorporated critically depends on the exposure time of the InP surface to the AsH 3 ambiance. And As atoms which replace P atoms in the monolayer of the surface are easily evaporated in the PH 3 ambiance, but it is difficult to remove the incorporated As atoms inside the grown InP layer even by a long PH 3 purge time.

Estimation of strain arising from the assembling process and influence of assembling materials on performance of laser diodes

A method for estimating strain in a semiconductor laser chip arising from bonding to foreign materials. The method is based on measurements of dependence of lasing wavelengths on duty ratios of pulsed operation with a constant peak current. The wavelength at zero duty ratio (λ0) is extrapolated from this dependence, from which the strain is estimated. Estimated strain from this method is in good agreement with result obtained from the change of polarization ratio, transverse‐magnetic to transverse‐electric light outputs. The strain arising from packaging affects not only lasing wavelength but also operating characteristics such as threshold current. Moreover, thermal resistance of laser diodes can be obtained from this dependence of lasing wavelengths on duty ratios.

High-power TQW AlGaAs laser with new inner-stripe structure

An approach to mass-production of triple quantum well lasers with a buried-ridge, loss-guided inner-stripe structure is demonstrated, using a large-scale metalorganic chemical vapor deposition. The lasers obtained from nine epi-wafers grown at one time show the uniform characteristics. In regard to high-power characteristics, the fundamental transverse mode up to 100mW and the maximum output power of - 170mW are realized at room temperature. Even at 95 C, the light output power of 100mW is obtained. The lasers have been operating over 1000 hours without failure at 6O C, 50mW. To realize the further uniformity and reproducibility of the laser characteristics, we have Introduced a newly developed etching method with an etching stop layer in the ridge formation.

High-power individually addressable monolithic four-beam array of GaAlAs window diffusion stripe lasers

A window structure has been applied, for the first time, to the individually addressable monolithic array of GaAlAs high-power lasers. A 100- mu m spaced array of four window diffusion stripe lasers with a long-cavity of 600 mu m has been fabricated by controllable open-tube two-step diffusion and single-step metalorganic chemical vapor deposition. The window structure and the p-type active stripes with a sufficiently narrow width around 2 mu m are formed by diffusion of zinc, which just passes through an n-type active layer. CW output power up to 120 mW without catastrophic damage and a threshold current around 30 mA have been achieved for each element in the wavelength range of 830 nm. Excellent uniformity of device characteristics across an array chip is confirmed. Thermal crosstalk of the elements operating simultaneously is investigated. >

Wavelength tunable 4-element laser array

A wavelength tunable 4-element laser array is fabricated with high performances suitable for the frequency division multiplexing (FDM) system. The array consists of four 1 .55 j.m DFB(distributed feedback) PPIBH (p-substrate partially inverted buried heterostructure) lasers with beam spacing of 125 jim. The lasing wavelength is tuned by changing the ratio of input currents to the two electrodes. The lasing frequency of the array can be allocated with a frequency interval of 10 GHz. An FM efficiency as large as 1 GHz/mA and a flat FM response with variation less than 3 dB in the modulation frequency range from 20 kHz to 1 GHz have been realized. An electrical crosstalk is less than -30 dB up to 800 MHz.

Effect of window diffusion stripe structure on reduction of temperature rise at laser facet

Abstract : Recently, optical data processing systems have increasingly required higher-power and more reliable short wavelength laser diodes. However, the major problem in high-power and long-term operation of the AlGaAs lasers is the degradation of the active layer In the vicinity of the mirror facet. This degradation is considered to be caused by heat generation due to the optical absorption resulting from the surface recombination at the mirror surface. The facet temperature rise of loss-guided stripe lasers such as a channeled substrate planar (CSP) laser was investigated, using laser Raman spectroscopy. It was confirmed that the optical absorption in the GaAs substrate outside the channel (stripe) region also increased the facet temperature, and the facet degradation began from the outside of the channel. On the other hand, a window diffusion stripe (WDS) laser has a non-absorbing region near the mirror and hardly absorbs the optical flux in the outside of the stripe region.

Fine-pitch control in EB lithography for semiconductor laser grating formation

Grating-pitch accuracy is studied from minimum pitch variation point of view. The pitches of the gratings delineated at the focus range from -50micrometers to +50micrometers and stitching errors between subfields are evaluated using an EB machine which features a long distance between the deflector and the wafer stage. The grating pitch variation is realized by using a deflection amplitude control. It is confirmed that errors of the pitches due to defocus are less than 0.05 nm, and the deviations from nominal setting of the pitch are also less than 0.1 nm when the pitches are varied from -6 percent to +6 percent at 0.1 percent step.