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Experimental and Theoretical Studies of Transient Electron Velocity Overshoot in GaN
Author(s) -
Wraback M.,
Shen H.,
Rudin S.,
Bellotti E.
Publication year - 2002
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/1521-3951(200212)234:3<810::aid-pssb810>3.0.co;2-w
Subject(s) - velocity overshoot , overshoot (microwave communication) , femtosecond , electron , electric field , transient (computer programming) , photoexcitation , saturation velocity , physics , rise time , steady state (chemistry) , condensed matter physics , atomic physics , field (mathematics) , materials science , drift velocity , optics , chemistry , voltage , excited state , quantum mechanics , laser , computer science , electrical engineering , operating system , engineering , mathematics , pure mathematics
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 ∼320 kV/cm, at which field a peak velocity of 7.25 × 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 electrons are primarily in the Γ valley. Full zone Monte Carlo calculations imply that the overshoot is associated more with band nonparabolicity in the Γ 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.