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Theoretical Study on Performance Limit of Cutoff Frequency in NanoScale InAs HEMTs Based on QuantumCorrected Monte Carlo Method
Takayuki TAKEGISHI Hisanao WATANABE Shinsuke HARA Hiroki I. FUJISHIRO
Publication
IEICE TRANSACTIONS on Electronics
Vol.E93C
No.8
pp.12581265 Publication Date: 2010/08/01 Online ISSN: 17451353
DOI: 10.1587/transele.E93.C.1258 Print ISSN: 09168516 Type of Manuscript: Special Section PAPER (Special Section on Heterostructure Microelectronics with TWHM 2009) Category: IIIV HighSpeed Devices and Circuits Keyword: quantumcorrected Monte Carlo, HEMT, InAs, InGaAs, delay time, cutoff frequency,
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Summary:
We theoretically study the performance limits of currentgain cutoff frequency, f_{T}, for the HEMTs with InAs or In_{0.70}Ga_{0.30}As middle layers in the multiquantumwell (MQW) channels by means of the quantumcorrected Monte Carlo (MC) method. We calculate the distribution of the delay time along the channel, τ(x), and define the effective gate length, L_{g,eff}, as the corresponding length to τ(x). By extrapolating L_{g,eff} to L_{g} = 0 nm, we estimate the lower limit of L_{g,eff}, L_{g}^{(0)}_{,eff}. Then we estimate the performance limit of f_{T}, f_{T}^{(0)}, by extrapolating f_{T} to L_{g,eff}^{(0)}. The estimated f_{T}^{(0)} are about 3.6 and 3.7 THz for the HEMTs with InAs middle layers of 5 and 8 nm in thickness, and about 3.0 THz for the HEMT with In_{0.70}Ga_{0.30}As middle layer of 8 nm in thickness, respectively. The higher f_{T}^{(0)} in the HEMTs with InAs middle layers are attributed to the increased average electron velocity, υ_{d}, in the channel. These results indicate the superior potential of the HEMTs using InAs in the channels. The HEMT with InAs middle layer of 8 nm in thickness shows the highest f_{T} on condition of the same L_{g} because of its highest υ_{d}. However, the increased total channel thickness results in the longer L_{g,eff}^{(0)}, which leads to the restriction of f_{T}^{(0)}. Therefore, in order to increase f_{T}^{(0)}, it is essential to make L_{g,eff} short in addition to making υ_{d} high. Our results strongly encourage in making an effort to develop the HEMTs that operate in the terahertz region.


