Camel-gate Field-effect Transistors Research Articles

Design consideration of [formula omitted]-doping channels for high-performance n + - GaAs / p + -InGaP/n-GaAs camel-gate field effect transistors

The influence of δ -doping channels on the performance of n +-GaAs/p +-InGaP/n-GaAs camel-gate field effect transistors is investigated by theoretical analysis and experimental results. The depleted pn junction of the camel gate and the existence of considerable conduction band discontinuity at the InGaP/GaAs heterojunction enhance the potential barrier height and the forward gate voltage. As the concentration–thickness products of the n-GaAs layer and δ -doping layer are fixed, the higher δ -doping device exhibits a higher potential barrier height, a larger drain current, and a broader gate voltage swing, whereas the transconductance is somewhat lower. For a n +=5.5×10 12 cm −2 δ -doping device, the experimental result exhibits a maximum transconductance of 240 mS/mm and a gate voltage swing of 3.5 V. Consequently, the studied devices provide a good potential for large signal and linear circuit applications.

Characteristics of a new camel-gate field effect transistor (CAMFET) with a composite channel structure

A new camel-gate field effect transistor (CAMFET) with a composite channel structure has been fabricated and demonstrated. Due to the n+-InGaP/p+-InGaP/GaAs camel gate and InGaAs/GaAs composite channel structures employed, good device performance is observed. Experimentally, at room temperature, a gate-drain breakdown voltage over 15 V, maximum transconductance gm,max of 111.5 mS mm−1, voltage gain AV of 93.4, unity current gain cut-off frequency fT of 16.2 GHz and maximum oscillation frequency unity fmax of 24.2 GHz are obtained simultaneously for a 1 × 100 µm2 device. The studied device also shows good properties in a higher temperature regime. Moreover, the studied device exhibits relatively negligible temperature-dependent characteristics over the operating temperature range from 300 to 420 K. Therefore, the studied device provides promise for high-temperature and high-performance microwave electronic applications.

InGaP/GaAs camel-gate field effect transistor with double δ-doping channel profiles

This paper presents the linearity enhancement of transconductance of an improved InGaP/GaAs camel-gate field effect transistor (CAMFET) with double δ-doping channel profiles. In this device, a low doped GaAs layer together with an n +-GaAs and an ultra-thin p +-InGaP layers form a high-performance camel gate structure. Also, double δ-doping channel profiles are used to enhance the output current and transconductance. For a 1 μm×100 μm CAMFET, a high breakdown voltage of 27 V, a maximum drain current of 770 mA mm −1, and a broad gate voltage range larger than 4 V with the intrinsic transconductance higher than 140 mS mm −1 are obtained. In addition, the measured unit current gain cutoff frequency f t is 14 GHz for the studied mesa type device. These results indicate the promise for high-performance large signal analog and digital switching, and high-frequency circuit applications.

Characteristics of GaAs/InGaP/GaAs doped channel camel-gate field-effect transistor

The characteristics of GaAs/InGaP/GaAs camel-gate field-effect transistor (CAMFET) with various channel structures including the single-, double-, and triple-step doped channel are studied. A theoretical model is used to analyze the device performances with different structures. Experimentally, a triple-step doped channel GaAs/InGaP/GaAs CAMFET has been fabricated successfully and demonstrated. From the theoretical analysis and experimental results, the gate turn-on and breakdown voltages could be enhanced by using the large band gap InGaP layer and triple-step doped channel structure. Furthermore, the good transistor characteristics are observed. Hence the studied device shows a good potential for the practice circuit applications.

Improved breakdown in LP-MOCVD grown n+-GaAs/(P+)-GaInP/n-GaAs heterojunction camel-gate FET

Fabrication of n/sup +/-GaAs//spl delta/(P/sup +/)-GaInP/n-GaAs heterojunction camel-gate field-effect transistors by LP-MOCVD is reported. The active channel was tri-step doped to obtain a high-barrier camel diode. A /spl delta/(P/sup +/)-GaInP layer was employed to offer a high valence band offset as a hole barrier, as well as an enhanced conduction band offset for good electron confinement. A camel diode using this material structure shows a barrier height >1.2 eV and a very high breakdown voltage of 33 V. The measured transconductance is 140 mS/mm with a unity current gain frequency of 17 GHz for a 1/spl times/50 /spl mu/m/sup 2/ device.

Multi-step doped-channel camel-gate FETs with a linear and enhanced transconductance

We report on the linear and enhanced transconductance by multi-step doped channel camel-gate field-effect transistors (CAMFETs) as compared with conventional CAMFETs. A low-doped layer along with the n + and p + layers is used to form a high-performance camel diode, which exhibits a large potential barrier so as not to drop rapidly. The measured barrier height is greater than 1.0 V. The measured gate-to-drain breakdown voltage at 1 mA/mm of gate current is about −21 V, whereas the rest layers doped heavily are used to enhance the transconductance and to improve the device linearity. A 1.5 x 100 μm 2 device has a peak transconductance of 220 mS/mm and a current density larger than 800 mA/mm. Furthermore, the device has a transconductance more than the peak value 80% over a wide drain current range from 160 to 800 mA/mm. The improvement of device linearity and the enhancement of current density suggest that the multi-step doped-channel F FETs are very promising far high power large signal circuit applications.

Influence of channel doping-profile on camel-gate field effect transistors

We report the performance of GaAs camel-gate FETs and its dependence on device parameters. In particular, the performance dependence on the doping-profile of a channel was investigated. In this study, one-step, bi-step, and tri-step doping channels with the same doping-thickness product are employed in camel-gate FETs, while keeping other parameters unchanged, For a one-step doping channel FET, theoretical analysis reveals that a high doping channel would provide a large transconductance which is suitable for logic applications. Decreasing the channel concentration increases the drain current and the barrier height. For a tri-step doping channel FET, it is found that the output drain current and the barrier height remain large and the relatively voltage-independent transconductance is also increased. These are the requirements for the large input signal power amplifiers. A fabricated camel-gate FET with a tri-step doping channel exhibits a large drain current density larger than 750 mA/mm and a potential barrier greater than 1.0 V. Furthermore, the relatively voltage-independent transconductance is as high as 220 mS/mm and the applied gate voltage is up to +1.5 V. A 1.5/spl times/100 /spl mu/m/sup 2/ device is found to have a f/sub t/ of 30 GHz with a very low input capacitance.

Characteristics of camel-gate structures with active doping channel profiles

In this paper, we demonstrate the influence of channel doping profile on the performances of camel-gate field effect transistors (CAMFETs). For comparison, single and tri-step doping channel structures with identical doping thickness products are employed, while other parameters are kept unchanged. The results of a theoretical analysis show that the single doping channel FET with lightly doping active layer has higher barrier height and drain-source saturation current. However, the transconductance is decreased. For a tri-step doping channel structure, it is found that the output drain-source saturation current and the barrier height are enhanced. Furthermore, the relatively voltage independent performances are improved. Two CAMFETs with single and tri-step doping channel structures have been fabricated and discussed. The devices exhibit nearly voltage independent transconductances of 144 mS mm −1 and 222 mS mm −1 for single and tri-step doping channel CAMFETs, respectively. The operation gate voltage may extend to ± 1.5 V for a tri-step doping channel CAMFET. In addition, the drain current densities of > 750 and 405 mA mm −1 are obtained for the tri-step and single doping CAMFETs. These experimental results are inconsistent with theoretical analysis.

Normally-on and normally-off camel diode gate GaAs field effect transistors for large scale integration

Normally-off and normally-on camel gate GaAs field effect transistors have been fabricated from structures grown by molecular beam epitaxy. These new devices use a camel diode gate formed from n+ and p+ layers instead of a Schottky barrier gate as used in metal-semiconductor field effect transistors. The camel diode gate provides these devices with several advantages over metal-semiconductor field effect transistors, including elimination of the metallurgical difficulties of the metal-semiconductor contact, relatively easy adjustment of the built-in voltage, and the potential for improved reliability in adverse environments and under conditions of high power dissipation. Fabrication of these devices does not require precision etching, making them compatible with large scale integrated circuit technology. Fabricated devices have yielded transconductances of 80 ms/mm in long channel (3 μm gate length) normally-on and normally-off field effect transistors and of 120 ms/mm in short channel (1 μm gate length) normally-on field effect transistors. Significantly improved gate-drain breakdown voltages and, in devices with AlxGa1−xAs buffer layers, excellent saturation characteristics have been observed. A simple theory providing analytical expressions describing the performance of normally-on and normally-off camel gate field effect transistors has been developed and good agreement with experiment has been obtained.