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Comment on Quantum capacitance of resonant tunneling diodes

2 pages
COMMENTS Comment on “Quantum capacitance of resonant sufficiently smooth so that variations in RI and R2 can be tunneling diodes” neglected within the range SV. Both assumptions are valid in the situation considered by HS. Serge Luiyi The time-dependent response SQ is easy to evaluate by AT&T Bell Laboratories, Murray Hill, New Jersey 07974 the standard methods. For an arbitrary t > 0 the result is (Received 26 February 1991) given by sQ(t)=sQ,(l -e-“T), (1) In a recent letter’ Hu and Stapleton (HS) introduced a quantity they call the quantum capacitance of resonance where tunneling (RT) diodes. This quantity, which I shall denote R,Cl- R2C2 by CHs, describes the modulation of charge SQ stored in SQ,=sV R t-R =cHSsvj (2) the quantum well (QW) in response to a variation of ex- 1 2 ternal voltage 6V applied to the diode, SQ= C&S V. HS RIMG + C2) assert that it is CHs rather the geometric barrier capaci- FE (3) RI-F& ’ tances C, =.cS/d, and C2=cY/d2 that determines the time constant of an RT oscillator. Proceeding to calculate Cns We see that Cns determines the magnitude of the stored in a simple model of a RT diode, HS find that charge in the steady state but not the small-signal dynam- Cns.@Z1,C,, and in this context they criticize my earlier ics. The “quantum capacitance” can be positive or nega- work.2 My problem with the HS letter is not that they had tive, but the approach to the steady state is characterized calculated their “quantum capacitance” ...
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