We study the covariant entropy bound in the context of gravitational collapse. First, we discuss critically the heuristic arguments advanced by Bousso. Then we solve the problem through an exact model: a Tolman-Bondi dust shell collapsing into a Schwarzschild black hole. After the collapse, a new black hole with a larger mass is formed. The horizon, L, of the old black hole then terminates at the singularity. We show that the entropy crossing L does not exceed a quarter of the area of the old horizon. Therefore, the covariant entropy bound is satisfied in this process.
High output power (above 3 mW/facet) AlGaAs/GaAs Transverse-Junction Stripe light emitting diodes have been grown on Semi-Insulating (100) GaAs substrates by Liquid Phase Epitaxy. These light emitting diodes utilize a "Direct-connecting" transverse-junction stripe structure, which can confine the transverse-current and reduce the series resistance. By thinning the thickness of the "effective active-layer'' of this structure, a room-temperature pulsed lasing operation is also achieved with a threshold current as low as 35 mA and a peak wavelength around 904 nm. This "Direct-connecting" transverse-junction stripe structure may be a pathway to monolithically integrate a Transverse-Junction Stripe light emitting device with a Metal-Semiconductor Field Effect Transistor on an electrical isolated semi-insulating substrate in the future.
Hg1−xCdxTe epitaxial layers were grown on CdTe substrates by the liquid-phase-epitaxy method in a horizontal open system. A semiclosed rotational boat was developed to prevent Hg loss from the Te-rich growth melt during growth processes. The solid composition of HgTe-rich Hg1−xCdxTe layers can be reproducibly controlled. Through the rotation mechanism, the melt entrapment on the as-grown surface can be avoided. With a small amount of excess Hg added into the growth melt and in situ annealing at 300 °C right after the growth, an n-type epilayer can be obtained. The electron concentration of 3×1015 cm−3 and the electron mobility of 7.5×104 cm2/V s were obtained.
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