| Summary: | 碩士 === 中國文化大學 === 材料科學與製造研究所 === 89 === Abstract
A noise model for High Electron Mobility Transistor (HEMT) or Modulation Doped Field Effect Transistor (MODFET) had been presented [37, 38]. The model is based on a self-consistent solution of the Schrödinger and Poisson’s equations. The self-consistent calculation allows us to characterize the quantum well (QW) properties for this class of devices. These include the average distance of the Two Dimensional Electron Gas (2DEG) and the Fermi level , as a function of 2DEG concentration .
An analytical model is used to investigate properties of the two-dimensional electron gas (2DEG) confined in a GaAs/AlGaAs quantum well (QW) formed in a Inverted High Electron Mobility Transistor (IHEMT). The position of the Fermi level and the average distance of the carriers in the well have been calculated as a function of the 2DEG concentration, ns. A charge control model has presented by Anwar et al. [37, 38] based on the self-consistent solution of Schördinger and Poisson’s equation. The results show a unique behavior of the average distance of the 2DEG increases with ns, a property unique to these types of structures. The analysis is extended to model current-voltage characteristics.
Instead of using a two-line or an exponential approximation to the velocity-electric field ( ) characteristic, an improved is used in this noise model. In addition, the reduced potentials are used to make the device D.C. current-voltage characteristic, small-signal parameters and noise properties analysis in nature.
The analysis of noise in this research can be outlined as: (a) calculation of thermal noise in the linear and saturation region of the channel, (b) evaluation of induced gate current noise in the linear and saturation region of the channel, (c) calculation of noise coefficient for different noise sources, such as P and R which are the noise coefficients for drain and gate noise, respectively and (d) the calculation of the correlation coefficient between different noise sources. Based on the equivalent noise circuit in terms of all noise sources and device small signal parameters, and accounting for all noise sources and their correlation, the minimum noise figure and minimum noise temperature are calculated. The calculated results are compared to the experimental data. The results show excellent agreement between the proposed theory and experimental data.
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