Metal-(n) AlGaAs-GaAs two-dimensional electron gas FET

Theoretical calculations have been developed for a two-dimensional electron gas FET (TEGFET) constituted by a AlGaAs (n)-GaAs (n^-or p^-) heterostructure in which the Schottky gate is deposited on the AlGaAs(n) top layer. The theory takes into account: i) the subband splitting in the two-dimensional electron gas (2-DEG); and ii) the existence of an undoped AlGaAs spacer layer which has been found to enhance the electron mobility. The sheet carrier concentration of the TEGFET has been calculated, and a simple analytical formula has been established for the charge control in large and small gate FET.     

Two-dimensional electron gas (2-DEG) interaction in adouble-heterostructure selectively contacted field-effecttransistor

Experimental results concerning the interaction between two two-dimensional electron gases (2-DEGs) in a single-quantum-well AlGaAs/GaAs/AlGaAs heterostructure field-effect transistor are presented. The results of magneto-transconductance measurements clearly delineate the behavior of low-field carrier mobilities in the two 2-DEG systems. The drain current/voltage characteristics clearly demonstrate that at 300 K the two 2-DEG systems interact, and at 77 K there is negligible interaction between the two 2-DEG systems under low-field conditions of operation     

Modelling of a depletion-mode MOSFET

A new depletion-mode MOSFET model is derived which includes the effects of the diffusion current along the channel and the actual band-bending at the semi-conductor surface. Because of the latter, a single drain current equation is obtained for the device operating in the linear region, irrespective of whether the channel surface is in accumulation or depletion. A separate equation for the diffusion current is also derived. Numerical results indicate that diffusion current is not significant in the linear regime of operation and, by extrapolation, in saturation.     

A charge-sheet analysis of short-channel enhancement-mode MOSFETs

A charge-sheet analysis of the short-channel MOSFET is presented. The expression achieved for the drain current, which takes into account both the drift and the diffusion components and also mobility degradation effects, holds in the strong-inversion, weak-inversion, and saturation regimes of the device operation, and results in a continuous function of all bias voltages. The model predicts an exponential dependence of the drain current on drain voltage in weak inversion and the threshold dependence on both channel length and drain voltage. Moreover, the proposed approach predicts results which satisfactorily compare with numerical simulations obtained from the two-dimensional analyzer MINIMOS and experimental data.     

HEMT器件小信号模型研究

提出一种AlGaAs/GaAs HEMT器件沟道电荷新模型,该模型用一个通用解析函数中系数的不同值来描述二维电子气(2DEG)和AlGaAs层中的电子浓度。在小信号特性上,除考虑了2DEG层外,又在考虑了AlGaAs层、速度饱和、饱和区沟道长度调制效应和源、漏串联电阻RS和RD等效应的基础上,推导出直流特性、跨导、输出电导和栅电容的解析表达式。仿真说明,在较大的栅、漏压范围内,该模型的理论值与实验结果符合良好。     

Monolithic integration of a 94 GHz AlGaAs/GaAs 2-DEG mixer onquartz substrate by epitaxial lift-off

In this paper, we report the integration of an AlGaAs/GaAs two-dimensional electron gas (2-DEG) bolometric mixer and a quartz-based microstrip circuit using the epitaxial lift-off (ELO) technique. The 1 μm thick high-mobility 2-DEG device transplanted on quartz showed no sign of degradation resulting from the ELO process. The 2-DEG mixer fabrication procedure demonstrated here is advantageous for its simplicity and uncritical choice of substrate. We obtained a minimum intrinsic conversion loss of 17 dB at 94 GHz at liquid nitrogen temperature. The measured IF bandwidth of the mixer was greater than 3 GHz     

On the charge control of the two-dimensional electron gas foranalytic modeling of HEMTs

A simple charge control model is developed for the two-dimensional electron gas (2-DEG) of high-electron-mobility transistors (HEMTs). This model explicitly takes into account the effective distance of the 2-DEG from the heterointerface and has been developed for use in analytic I-V and C-V modeling. In this model, the Fermi energy level versus the 2-DEG sheet carrier-concentration is represented by a simplified expression derived from the triangular potential well approximation and is shown to be dominated by terms with different functional forms in two distinct operation regions: a moderate carrier-concentration region and a subthreshold region. The validity of the analytic charge control model is supported by the calculated results of a self-consistent quantum mechanical model     

A calibrated model for the subthreshold operation of a short channel MOSFET including surface states

Describes a simple two-dimensional subthreshold model for short channel MOSFET's. The effects of surface state density are also included in the model. A regional charge density approximation was used in the solution of Poisson's equation and an analytical solution of the continuity equation in two dimensions was derived. Excessive computations are avoided in the present model; this was made possible by the use of a valid regional charge approximation. The model was experimentally verified by performing measurements on short channel devices. The model was calibrated from measurements on a long channel device which was present on the same silicon chip. Results are presented for the subthreshold leakage current as a function of substrate bias, polysilicon gate length, diffusion depth and surface state density.     

An analytical threshold voltage and subthreshold current model forshort-channel AlGaAs/GaAs MODFETs

Short-channel effects on the subthreshold behavior are modeled in self-aligned gate AlGaAs/GaAs MODFETs through an analytical solution of the two-dimensional Poisson equation in the subthreshold region. Based on the resultant potential solution, simple and accurate analytical expressions for short-channel threshold voltage, subthreshold swing, and subthreshold drain current are derived. These are then used to develop an expression for minimum acceptable channel length. A comparative study of short-channel effects in enhancement-mode MODFETs with and without i-AlGaAs spacer layers indicates that channel lengths will be limited to 0.18-0.25 μm by subthreshold conduction. Minimum gate lengths for MODFETs with a spacer layer are notably larger than those without a spacer layer. Besides offering insights into the physics of short-channel effects in MODFETs, the model provides a useful basis for efficient design, analysis, and simulation of small geometry AlGaAs/GaAs MODFET digital circuits     

An analytical and computer-aided model of the AlGaAs/GaAs high electron mobility transistor

An analytical model for the AlGaAs/GaAs high electron mobility transistor (HEMT) or MODFET has been developed. This model uses a Trofimenkoff-type relation [1] for the electron velocity and electrical field and assumes that the electron velocity saturation inside the two-dimensional electron gas channel cause current saturation. It also takes into account the parasitic conduction in the AlGaAs layer by including a MESFET operation. Based on this model, analytical current-voltage equations suitable for computer simulation have been derived. Calculated results for sub-half-micrometer HEMT's show excellent agreement with measured characteristics.     

Large transconductance n+-Ge gate AlGaAs/GaAs MISFET with thin gate insulator

The effects of insulator layer thickness on an n+-Ge gate MISFET were studied. The transconductance increases with decreasing AlGaAs layer thickness from 60 down to 10 nm. From the variation of the intrinsic transconductance, the effective insulator layer thickness was found to be enlarged by about 9 nm. This is due to the finite width of two-dimensional electron gas (2-DEG). A large transconductance of 430 mS/ mm was obtained at room temperature for the 0.8-µm gate-length FET with 10-nm-thick AlGaAs. This large transconductance demonstrates the inherent potential of the n+-Ge gate MISFET for LSI application.     

Analysis of the depletion-mode MOSFET including diffusion and drift currents

A four-terminal model for a long-channel depletion-mode MOS transistor including both the diffusion and the drift components of the current along the channel is developed. The theory, which is derived in the gradual channel hypothesis, has been built-up by considering both Poisson's equation and the current-continuity equation. The model is able to describe, without discontinuities, the dc drain current in the enhancement, depletion, and subpinchoff regimes of operation of the device. It is shown that pinchoff and zero drain conductance are naturally achieved as the drain voltage increases, while in the subpinchoff regime the drain current exponentially depends on gate voltage and is mainly due to the diffusion component. Finally, it is found that mobility degradation effects due to the normal component of the electric field can easily be taken into account and it is shown that experimental data favorably compare with the proposed model.     

A two-dimensional analysis of indium phosphide junction field effect transistors with long and short channels

A two-dimensional analysis of indium phosphide junction field effect transistors with long and short gates is presented. The two devices are shown to have properties similar to those of gallium arsenide JFETs. The short gate device has a negative resistance region at low drain voltages which is absent in the long gate device. The negative resistance region is determined by the distribution of the drift velocity along the conducting channel, and the resulting distribution of the electron charge. A field dependent mobility is used, and its effect on current saturation is discussed. The electrostatic charge distribution and electric field distribution are calculated for both devices, and are shown in graphic form.     

QUANTUM MECHANICAL MODEL AND SIMULATION OF GaAs／AlGaAs QUANTUM WELL INFRARED PHOTODETECTOR—Ⅱ ELECTRICAL ASPECTS

ＩｎｔｒｏｄｕｃｔｄｏｎＩｎｔｈｅｆｉｒｓｔｐａｒｔ ,ｗｅｈａｖｅｄｉｓｃｕｓｓｅｄｔｈｅｏｐｉｔｉｃａｌａｓｐｅｃｔｓａｂｏｕｔｔｈｅｑｕａｎｔｕｍｗｅｌｌｉｎｆｒａｒｅｄｐｈｏｔｏｄｅｔｅｃ ｔｏｒ .Ｈｅｒｅｗｅｃｏｎｔｉｎｕｅｄｉｓｃｕｓｓｉｏｎｓａｂｏｕｔｔｈｅｅｌｅｃｔｒｉｃａｌａｓｐｅｃｔｅｓｏｆｔｈｅｄｅｖｉｃｅｍｏｄｅｌａｎｄｓｉｍｕｌａｔｉｏｎ .1　ＤａｒｋＣｕｒｒｅｎｔａｎｄＰｈｏｔｏｃｕｒｒｅｎｔＤｉｓｔｒｉｂｕｔｅｄｅｆｆｅｃｔｓｏｆｅｘｔｅｒｎａｌｂｉａｓａｃｒｏｓｓｔｈ…     

Charge control, DC, and RF performance of a 0.35-μmpseudomorphic AlGaAs/InGaAs modulation-doped field-effecttransistor

The authors describe a study of charge control in conjunction with DC and RF performance of 0.35-μm-gate-length pseudomorphic AlGaAs/InGaAs MODFETs. Using C-V measurements, they estimate that a two-dimensional electron gas (2DEG) with density as high as 1.0×10¹² cm^-2 can be accumulated in the InGaAs channel at 77 K before the gate begins to modulate parasitic charges in the AlGaAs. This improvement in charge control of about 10-30% over a typical AlGaAs/GaAs MODFET may partially be responsible for the superior DC and RF performance of the AlGaAs/InGaAs MODFET. At room temperature, the devices give a maximum DC voltage gain g _m/g_d of 32 and a current gain cutoff frequency f_T of 46 GHz. These results are state of the art for MODFETs of similar gate length     

Nonlinear charge control in AlGaAs/GaAs modulation-doped FET's

A new model for nonlinear charge control in normally on modulation-doped field-effect transistors (MODFET's) is proposed. It is shown that conventional charge control models are insufficient to describe MODFET's with large negative pinchoff voltages, and that the depletion approximation is inaccurate in circumstances where the layer dimensions become of the order of a Debye length. The new model is based upon a one-dimensional numerical solution of Poisson's equation and the drift-diffusion equation. It also takes into account the shift in the 2DEG position with gate bias, and parallel conduction in the doped AlGaAs layer. The effect of nonlinear charge control on MODFET transconductance is considered by combining the new model with a two-dimensional analytic representation of the MODFET.     

Current—voltage characteristics of an AlGaAs/GaAs heterostructure FET for high gate voltages

Drain-to-source current for high gate voltages in AlGaAs/GaAs heterostructure FET's (HFET's) is found to depend on the electron saturation velocity in the AlGaAs layer. A simple model, which takes into account the current through the undepleted channel in the AlGaAs layer as a function of the electron saturation velocity in AlGaAs, is proposed for describing I-V characteristics of HFET's for high gate voltages. Using the model, effective electron saturation velocity in AlxGa1-xAs for different Al content levels has been obtained from the analysis of the present experimental results; 7 × 10⁶cm/s for x = 0.24 and 3 × 10⁶cm/s for x = 0.3 at a 4 × 10¹⁷cm^-3doping concentration.     

An accurate HJFET capacitance-voltage model for implementation witha circuit simulator

We present a new accurate HJFET capacitance model to implement with a circuit simulator. This is an analytical model that describes capacitance-voltage (C-V) characteristics over a wide supply voltage range. The model for a capacitance component due to two-dimensional electron gas (2-DEG) conduction is based on gradual channel approximation, and takes into account the gradual capacitance transition near the threshold voltage. It also takes into account the field dependence of the 2-DEG mobility, which is very strong for deep sub-micron devices. The model for parasitic MESFET capacitance is based on the formula for a Schottky diode. Since the model consists of physical parameters, it provides feedback between the fabrication process and circuit design. The simulated results agree well with the measurements     

QUANTUM MECHANICAL MODEL AND SIMULATION OF GaAs/AlGaAs QUANTUM WELL INFRARED PHOTO- DETECTOR-Ⅰ OPTICAL ASPECTS

ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｆｒａｒｅｄｄｅｔｅｃｔｏｒｔｅｃｈｎｉｑｕｅｈａｓｂｅｅｎａｋｅｙｆａｃｔｏｒｉｎｔｈｅｄｅｖｅｌｏｐｍｅｎｔｏｆｔｈｅｉｎｆｒａｒｅｄｔｅｃｈｎｏｌｏｇｙｆｏｒｍｏｒｅｔｈａｎ 4 0 ｙｅａｒｓ .Ｓｉｎｃｅ 1970 ,ｓｅｍｉｃｏｎｄｕｃｔｏｒｓｌｉｋｅＩｎＳｂａｎｄＨｇＣｄＴｅｈａｖｅｂｅｅｎｔｈｅｐｒｉｎｃｉｐａｌｍａｔｅｒｉａｌｓｆｏｒｖａｒｉｏｕｓｉｎｆｒａｒｅｄｄｅｔｅｃｔｏｒａｐｐｌｉｃａｔｉｏｎｓ .Ｔｈｅｆｏｒｍａｔｏｆｔｈｅｉｎｆｒａｒｅｄｄｅｔｅｃｔｏｒｍｏｔｉｖａｔｅｄｂｙｓｍａｒｔｔｈｅｒｍａｌｉｍａｇｉｎｇｓｙｓｔｅｍｃｈａｎｇｅｄｆｒｏｍｓｉｎｇｌｅｅｌｅｍｅｎｔｄｅｖｉｃｅｔｏｆｏｃａｌｐｌａｎａｒｒａｙｓ(ＦＰＡｓ)ｉｎｔｈｅｍｉｄｄｌｅｏｆ 80’ｓ [1].Ｔｏｄａｙ’ｓｔｅｃｈｎｏｌｏｇｙｏｆｉｎｆｒａｒｅｄｄｅｔｅｃｔｏｒｃｏｎｃｅｎｔｒａｔｅｓｌａｒｇｅｌｙｏｎｆｏｃａｌｐｌａｎａｒｒａｙｓ ,ｅｘｐｅｃｉａｌｌｙｆｏｒｓｅｎｓｉｔｉｖｅ ,ｈｏｍｏｇｅｎｅｏｕｓａｎｄｌａｒｇｅｆｏｒｍａｔｓｃａｌｅｄｅｖｉｃｅｓ .ＨｇＣｄＴｅ...     

A quantum-dot heterostructure transistor with enhanced maximum drift velocity of electrons

A new type of heterotransistor based on an AlGaAs/GaAs/InAs/GaAs/InAs structure with a layer of InAs quantum dots embedded directly into the GaAs channel is fabricated. High values of the maximum saturation current (up to 35 A/cm) and transconductance (up to 1300 mS/mm) are attained. The specific features of the current-voltage characteristics of the new device are explained in the context of a model that takes into account the ionization of quantum dots in high electric fields and tenfold enhancement of the electron drift velocity in a structure with an InAs quantum-dot layer in the vicinity of an AlGaAs/GaAs heterojunction.