Hiroo Yonezu

An AlGaAs window structure laser

Extremely high optical power density emission was achieved with an AlGaAs window structure laser in CW operation as well as pulsed operation by increasing the threshold of the catastrophic optical damage (COD) on mirrors. A Zn diffused window stripe laser consists of the Zn diffused p-type light emitting region with low effective energy gap in the central part and the n-type window regions with high effective energy gap at both ends of the cavity. The maximum available optical power in pulsed operation was at least one order of magnitude higher than the COD threshold in conventional structures. 80 mW optical power in CW operation was achieved in the Zn diffused window stripe laser with a 5 μm wide stripe. Furthermore, gradual degradation due to the photoenhanced mirror oxidation has been reduced significantly under long term CW operation.

Degradation mechanism of (Al · Ga)As double‐heterostructure laser diodes

This paper reports new observations in degraded (Al · Ga)As double‐heterostructure (DH) laser diodes and proposes a mechanism of short‐term ([inverted lazy s] 100 h) degradation characteristic to DH structures. Degradation is seen localized as ``dark lines of certain crystalline orientations in electroluminescent patterns, as well as junction current patterns using an SEM. X‐ray measurement showed internal strain due to heteromismatch. It is suggested that the internal stress accelerates development of the dark lines, which is likely to be a crystalline defect caused by thermal stresses.

Computer-aided design of a Si avalanche photodiode

A computer-aided design of a Si avalanche photodiode is presented. As an example, the design of the boron diffused photodiode with a desired time constant is carried out. The choice of an area of an active region is not affected by a diffusion condition but primarily by a substrate impurity concentration. For a very high speed response a moderate substrate impurity concentration must be selected. For a longer time constant than about 0.1 ns an increasing area of an active region is acceptable with a decreasing substrate impurity concentration. In a lightly doped substrate, a uniform multiplication of an active region cannot occur. Using the usual diffusion technique the acceptable highest resistivity of a substrate is about 1-2 Ω.cm. The capacitance of the guard ring occupies a considerable part in a total capacitance. Calculated results are in good agreement with experimental results.