Daijiro Inoue

High-power 200 mW 660 nm AlGaInP laser diodes with low operating current

We have newly introduced a two-step-growth structure and a ridge stripe with steep sidewalls formed with a dry-etching process in the fabrication of a buried ridge stripe structure of a high-power 660 nm laser diode instead of a conventional three-step-growth structure and a ridge stripe with gentle sidewalls formed with a conventional wet-etching process in order to reduce the operating current. We have found that the two-step-growth structure provides better heat dissipation and the dry-etched ridge stripe structure offers higher characteristic temperature. The operating current under pulsed 200 mW at 70°C of the fabricated laser diode is 270 mA. This is the lowest value ever reported so far, to our knowledge. These laser diodes exhibit a kink level and a maximum light output power of 220 mW and higher than 300 mW, respectively. These laser diodes have also operated stably for 1500 h at 70°C with a light output power of 200 mW under the pulsed condition.

Reduction in Operating Current of High-Power 660 nm Laser Diodes Using a Transparent AlGaAs Cap Layer.

We have introduced a transparent AlGaAs cap layer instead of a conventional GaAs cap layer into high-power 660-nm-band-laser diodes with weaker optical confinement in the perpendicular direction, since this structure enables us to weaken the optical confinement without increasing the internal loss for a real index-guided structure. The fabricated laser diodes have demonstrated reduced operating current of 150 mA at 100 mW and increased maximum light output power of 200 mW under the pulsed condition. An aspect ratio of 1.5, which is the smallest of all 660-nm-band high-power laser diodes reported to date, has also been achieved. These laser diodes have been operating stably under the pulsed condition for nearly 2000 h at 60°C with a light output power of 100 mW, which is also the highest of all real index-guided 660-nm-band laser diodes reported to date.

A New High Electron Mobility Transistor (HEMT) Structure with a Narrow Quantum Well Formed by Inserting a Few Monolayers in the Channel

A new HEMT wafer has been developed whose channel layer has a narrow bandgap semiconductor with a few monolayers inserted at an optimum position in the channel, namely, the point where the probability density of electrons is maximum in the lowest subband and negligible in the first excited subband. The Al0.22Ga0.78As/In0.15Ga0.85As pseudomorphic HEMT wafer with one InAs monolayer inserted at the optimum position has provided Hall electron mobility increments nearly 15% higher at 300 K and 20% higher at 77 K than those of conventional pseudomorphic HEMT wafers.

A new two-mode channel FET (TMT) for super-low-noise and high-power applications

A super-low-noise two-mode channel FET (TMT) with high- and plateau-shaped transconductance (g/sub m/) characteristics has been developed. It has two electron transport modes against the applied gate voltage (V/sub gs/). That is, the electrons mainly drift in a highly doped channel region at a shallow V/sub gs/. A plateau g/sub m/ region and the maximum g/sub m/ were achieved at a V/sub gs/ range of -0.25 approximately +0.5 V and 535 mS/mm, respectively. The minimum noise figure and associated gain for the TMT were superior in the low-drain-current (I/sub ds/) region and nearly equal in the middle and high I/sub ds/ region to those of an AlGaAs/InGaAs pseudomorphic HEMT fabricated using the same wafer process and device geometry.<<ETX>>

High-Power 660-nm-Band AlGaInP Laser Diodes with a Small Aspect Ratio for Beam Divergence

High-power 660-nm-band AlGaInP laser diodes with a small aspect ratio have been successfully fabricated with a window-mirror structure. The relationship between optical confinement in the perpendicular direction and internal loss was investigated, and a real index-guided structure with an AlInP current blocking layer was applied on the basis of this investigation. A high-power laser diode with a small aspect ratio of 1.65 for beam divergences of 16.5° and 10° in the perpendicular and parallel directions, respectively, has shown a high kink level of 160 mW and a high maximum light output power of 180 mW under pulsed condition. These laser diodes have operated stably for more than 1500 h with a light output power of 90 mW at 60°C under pulsed condition. Stable pulsed operation at 60°C with a high power of 90 mW and small aspect ratio of 1.65 have been simultaneously achieved for the first time.

Influence of rapid thermal annealing on modulation doped structures

Abstract We have investigated the influence of high temperature annealing on modulation doped structures of AlGaAs/GaAs, AlGaAs/InGaAs and InAlAs/InGaAs systems grown by molecular beam epitaxy. Hall-measurement reveals reduction in two-dimensional electron gas mobility and almost unchanged sheet density after annealing at 800–880°C for 5 s in each hetero-junction system. The mobility reduction is enhanced with the increase in annealing temperature and with the decrease in thickness of a spacer between a donor layer and a channel layer. This behavior is attributed to diffusion of Si dopants from a donor layer to a spacer layer resulting in an increasing ionized impurity scattering effect. It is found that In contained structures especially an InP-based InAlAs/InGaAs structure, provide both large 2DEG sheet density and excellent thermal stability of the modulation doped structure.

High-power GaN-based blue-violet laser diodes

We have succsessfully developed blue-violet laser diodes having the worlds highest output power of 450mW by introducing a novel facet coating structure, reducing the internal loss in devices, and making a cavity length long.

A Superlow-Noise AlGaAs/InGaAs/GaAs Doped Channel Heterojunction Field-Effect Transistor (DC-HFET) with 0.15-µm Gate Length

A doped channel heterojunction field-effect transistor (DC-HFET) has been developed using an AlGaAs/InGaAs/GaAs pseudomorphic system which has an electron confinement effect superior to that of an AlGaAs/GaAs system. An excellent minimum noise figure (NFmin) of 0.65 dB and associated gain (Ga) of 11.3 dB were realized at 12 GHz (drain current (Ids)=18 mA, drain voltage (Vds)=2 V). The NF had weak dependences on the Ids and frequency, as in the case of high electron mobility transistors (HEMTs). The transconductance (gm) at Ids=10 mA was 385 mS/mm and maximum gm reached 570 mS/mm (Ids=50 mA).

Quantification of Electrical Deactivation by Triply Negative Charged Ga Vacancies in Highly Doped Thin GaAs Layers.

We present for the first time a theoretical approach to electrical deactivation by triply negative charged Ga vacancies (V 3- Ga in highly doped thin n-GaAs layers grown by molecular beam epitaxy, and quantify their deactivation under as-grown and annealed conditions. We also show that thinning of n-GaAs epitaxial layers results in low-level electrical deactivation. This effect is apparently caused by the fact that thinning of the doped layers results in lowering of the Fermi energy in the doped layers, and thereby inhibition of the generation of V 3- Ga acceptors. Furthermore, we deduce from the results of this study the thermal equilibrium concentration of V 3- Ga in intrinsic GaAs. The resulting expression is [V 3- Ga (i)] = 5.37 X 10 31 exp(-4.64eV/k B T) cm -3 .

Excellent Thermally Stable Epitaxial Channel for Implanted Planar-Type Heterojunction Field-Effect Transistors

We demonstrate for the first time that the decrease in the carrier concentration of highly doped GaAs layers caused by annealing is alleviated by thinning the layers. It is also suggested that the decrease is dependent on the Fermi energy in the doped layers. Thermally stable thin Si-doped GaAs channels are formed in implanted planar-type two-mode channel field-effect transistors (P-TMTs). A 0.2-μm device having a GaAs channel 9 nm thick with a doping level of 7 x 10 18 cm -3 exhibits excellent performance, such as a transconductance g m of 450 mS/mm, a current-gain cutoff frequency f T of 72 GHz, and a maximum frequency of oscillation f max of 140 GHz. Furthermore, it is indicated that highly doped thin layers are very effective for improving the DC and microwave performance of P-TMTs.