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Experimental and theoretical studies of transient electron velocity overshoot in GaN

机译：GaN中瞬态电子速度过冲的实验和理论研究

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We employ an optically detected time-of-flight technique with femtosecond resolution that monitors the change in the electroabsorption due to charge transport in an AlGaN/GaN heterojunction p-i-n diode to measure the electron velocity overshoot in GaN at room temperature. It has been found that electron velocity overshoot occurs at electric fields as low as 105 kV/cm, with the peak transient velocity increasing with E up to similar to320 kV/cm. at which field a peak velocity of 7.25 x 10(7) cm/s is attained within the first 200 fs after photoexcitation. At higher fields, the increase in transit time with increasing field suggests the onset of negative differential resistance due to intervalley transfer. The existence of transient velocity overshoot at fields lower than the calculated peak steady-state velocity suggests that it occurs while the electron, are primarily in the Gamma valley. Full zone Monte Carlo calculations imply that the overshoot is associated more with band nonparabolicity in the Gamma valley than with intervalley transfer at fields less than 325 kV/cm, and, in conjunction with theoretical calculations employing a semiclassical transport model, confirm the importance of this nonparabolicity for the determination of the temporal shape of the transient velocity overshoot curves. [References: 14]
机译：我们采用具有飞秒分辨率的光学检测飞行时间技术，该技术可监测AlGaN / GaN异质结p-i-n二极管中由于电荷传输而引起的电吸收变化，以测量室温下GaN中的电子速度过冲。已经发现，在低至105 kV / cm的电场下会发生电子速度过冲，峰值瞬态速度随E的增加而增加，直至接近320 kV / cm。在该电场下，光激发后的前200 fs内达到7.25 x 10（7）cm / s的峰值速度。在较高的磁场中，传输时间随磁场的增加而增加，这表明由于间隔转移而引起的负差分电阻的出现。在低于计算出的峰值稳态速度的场上，存在瞬态速度超调现象，这表明它是在电子主要位于伽马谷时发生的。全区蒙特卡洛计算表明，过冲与伽马谷地带的非抛物线性有关，而不是与在小于325 kV / cm的磁场中的间隔转移有关，并且与采用半经典输运模型的理论计算相结合，证实了这一点的重要性。非抛物线性，用于确定瞬时速度超调曲线的时间形状。 [参考：14]

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