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High‐efficiency and low‐threshold InGaAs/AlGaAs quantum‐well laser structures have been grown by molecular beam epitaxy. Material characterization was performed on polyimide‐planarized ridge‐waveguide lasers. The measured material gain data are compared to theoretical calculations that include the valence‐band mixing effects. Total injection current densities of 84 and 60 A/cm2 have been measured from 50‐μm‐wide laser diodes with cavity lengths of 2850 μm (from a double‐quantum‐well sample) and 1770 μm (from a single‐well sample), respectively. Moreover, we have also obtained a cw threshold current as low as 2.1 mA from a 1.7‐μm‐wide and 140‐μm‐long as‐cleaved ridge‐waveguide device. In addition, the lateral current leakage for the double‐quantum‐well sample is found to be twice that of the single‐well one.

Double heterostructure InGaAs‐GaAs strained‐layer single quantum well ridge waveguide lasers grown by molecular beam epitaxy were fabricated by using in situ laser monitored reactive ion etching to form the ridges. Continuous‐wave threshold current as low as 3.5 mA was obtained on a ridge laser diode of 3.3 μm wide and 215 μm long having cleaved mirrors. The lasing wavelength is at 0.988 μm and the measured differential external quantum efficiency is 61%.

Raman analysis of the A1 (LO) mode of AlGaN-like phonons of the InAlGaN/GaN heterostructures in the composition range 1.38% ≦ In ≦ 2.73% and 8.01% ≦ Al ≦ 13.97% is presented. The line shape of A1 (LO) mode of AlGaN-like phonons was observed to exhibit a significant asymmetry and Raman linewidth toward the lower energy side. The spatial correlation model is discussed and is shown to account the line shape. The spatial correlation model calculations also indicate the lack of a long-range order in the higher Al to In ratio of InAlGaN/GaN alloys. These results were confirmed by x-ray diffraction and the correlation length L decreases as the increasing of Al to In ratio corresponding to the absence of the long-range order in the alloy. The Raman linewidth of the AlGaN-like A1 (LO) mode was found to exhibit a maximum at the higher Al to In ratio indicative of a random disordered alloy system.

We report the observation of persistent photoconductivity (PPC) effect in 2H‐MoSe2 layered semiconductors. The decay behavior of PPC can be well described by a stretch-exponential function. Experimental results indicate that the lattice relaxation of DX-like impurity is responsible for PPC in MoSe2. In addition, the small capture barrier created by lattice relaxation and the temperature-dependent resistance measurement exhibit that the magnitude of PPC effect in MoSe2 is small, consistent with the PPC behavior in indirect gap materials.