We demonstrated the selective lasing of guided modes from hollow square microcavities having an InGaAsP/InGaAs quantum well gain layer. For hollow square cavities with symmetric convex corners, ring-type whispering gallery modes (WGMs) originating from total reflections of light at the four corners were lased. By modifying the corner shape to be asymmetric and concave, guided modes originating from total reflections at the inner and outer flat boundaries were selectively lased. We determined that the lasing modes were guided modes by analyzing measured spectra. The observed quality factor Q was smaller than that of ring-type WGMs owing to enhanced total reflection loss.

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We report on the breakdown voltages in InP/InGaAs avalanche photodiode (APD) experimentally and theoretically, based on the parameters of electric field distribution, carrier concentrations, thicknesses, and temperatures. According to the calculation, the breakdown voltage has its minimum point, w0, at each carrier concentration in charge plate and avalanche photodiode with very thin multiplication layer width will provide high gain bandwidth product. The devices having different multiplication layer width showed different breakdown voltages and temperature behaviors. We introduced newly defined temperature coefficient, γ, and found that γ’s are linearly dependent on breakdown voltages at each temperature. From these results, the empirical formula which effectively describes the temperature dependence of breakdown voltages was obtained.

This work reports the spectral characteristics of coupled square ring semiconductor resonators. For a single mode operation, the square ring cavities coupled with multimode interferometers (MMIs) are proposed and fabricated using the epitaxial layers of 1.55 microm center wavelength InGaAsP-InP multiple quantum wells. Resonant characteristics can be tailored by varying the parameters of the cavity size or the waveguide width. By using the MMI coupled square ring cavity, a stable single spectral lasing mode was obtained in various combinations of square cavities.

Breakdown voltages of InP/InGaAs avalanche photodiodes have been analyzed with structure parameters, such as multiplication layer width (MLW) and absorption layer thickness. It is shown that there exists a critical MLW, w0, where the breakdown voltage is the lowest. As MLW increases, the breakdown voltage increases slowly in the region of MLW≥w0 while the breakdown voltage decreases in the region of MLW≤w0. It is also revealed that w0 is a function of absorption layer thickness. The measured breakdown voltages having MLWs of 0.15–0.4 μm were reported and compared to the calculated ones, which agreed very well with each other.