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A time evolution method is used to compute the electron escape time and dark current of a quantum dot under electric field. We found that for quantum dots with just one bound state, the ground state wave function can be well described by the product of a 2D confined wave function in the x, y plane and a 1D confined wave function in the z direction with an effective quantum well potential. A comparison of phase-shift analysis and the full time-dependent calculation is presented. Good agreement between the two in the large time scale is found, but discrepancy exists in the small time scale. Our study shows that the electron escape rate (which determines dark current) of quantum dots is much lower than that of quantum wells with the same bound-to-continuum transition energy.
We present a device fabrication technology and measurement results of both optically pumped and electrically injected InGaN/GaN-based distributed feedback (DFB) lasers operated at room temperature. For the optically pumped DFB laser, we demonstrate a complex coupling scheme for the first time, whereas the electrically injected device is based on normal index coupling. Threshold currents as low as 1. 1 A were observed in 500 μm long and 10 μm wide devices. The 3rd order grating providing feedback was defined holographically and dry-etched into the upper waveguiding layer by chemically-assisted ion beam etching. Even when operating these lasers considerably above threshold, a spectrally narrow emission (3.5 Å) at wavelengths around 400 nm was seen.
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