Chung-I Kao

Influences of sulfur passivation on temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs PHEMT

The influences of (NH/sub 4/)/sub 2/S/sub x/ treatment on an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) are studied and demonstrated. Upon the sulfur passivation, the studied device exhibits better temperature-dependent dc and microwave characteristics. Experimentally, for a 1/spl times/100 /spl mu/m/sup 2/ gate/dimension PHEMT with sulfur passivation, the higher gate/drain breakdown voltage of 36.4 (21.5) V, higher turn-on voltage of 0.994 (0.69) V, lower gate leakage current of 0.6 (571) /spl mu/A/mm at V/sub GD/=-22 V, improved threshold voltage of -1.62 (-1.71) V, higher maximum transconductance of 240 (211) mS/mm with 348 (242) mA/mm broad operating regime (>0.9g/sub m,max/), and lower output conductance of 0.51 (0.53) mS/mm are obtained, respectively, at 300 (510) K. The corresponding unity current gain cutoff frequency f/sub T/ (maximum oscillation frequency f/sub max/) are 22.2 (87.9) and 19.5 (59.3) GHz at 250 and 400 K, respectively, with considerably broad operating regimes (>0.8f/sub T/,f/sub max/) larger than 455 mA/mm. Moreover, the relatively lower variations of device performances over wide temperature range (300/spl sim/510 K) are observed.

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 ?m2 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.

Comprehensive Temperature-Dependent Studies of Metamorphic High Electron Mobility Transistors With Double and Single

The temperature-dependent characteristics of meta morphic high electron mobility transistors (MHEMTs) with double and single δ-doped structure are studied and demonstrated. Due to the use of double δ-doped sheets, the current density in the channel layer and two-dimensional electron gas could effectively be increased. The excellent turn-on voltage of 1.18 (0.80) V, max imum drain saturation current of 544 (524) mA/mm, maximum extrinsic transconductance of 361 (312) mS/mm, unity current gain cutoff frequency of 55.06 GHz, and maximum oscillation frequency of 129.17 GHz are obtained at 300 (510) K for a 0.6 × 100 μm2 gate dimension double δ-doped MHEMT. In addition, using wide-bandgap InAlAs Schottky, spacer, and buffer layers, the carrier confinement could significantly be improved at high temperature. Therefore, excellent thermal stability is achieved for double δ-doped MHEMT. The device with a double δ-doped structure exhibits a considerably low temperature coefficient on threshold voltage (∂Vth/∂T) of 0.06 mV/K when the temperature is increased from 330 to 510 K, which is superior to previous reports of related high electron mobility transistors.

\delta

An interesting InGaP/InGaAs heterostructure field-effect transistor utilizing dual /spl delta/-doped quantum wells as double channels is studied and demonstrated. The employed dual /spl delta/-doped quantum wells and InGaP layer provide good carrier confinement and Schottky behavior, respectively. Good device performances including higher turn-on and breakdown voltages, high and linear transconductance and RF properties are obtained. For a 1 /spl times/ 100 /spl mu/m device, turn-on voltage of 1.74 V, maximum output current of 499 mA/mm, and maximum transconductance of 162 mS/mm with 303 mA/mm broad operation regime are obtained. The microwave properties of f/sub T/ and f/sub max/ are 16 and 32.3 GHz, respectively. Furthermore, even the device is operated at higher temperature regime (>400K), insignificant degradations of DC and RF performances are observed.

-Doped Structures

The device properties of InGaP/InGaAs double delta-doped channel heterostructure field-effect transistors (DDDCHFETs) are comprehensively analyzed and demonstrated. Based on the variations of delta-doped densities of InGaAs double channels and GaAs spacer thickness, the dc and rf characteristics are compared and studied. Due to the employed InGaAs DDDC structure and Schottky behaviors of InGaP “insulator,” good pinch-off and saturation characteristics, higher and linear transconductance, and good rf performances are obtained. Experimentally, for comparison, a practical DDDCHFET with good device properties is fabricated successfully. It is known that the experimental results are very consistent with theoretical simulation data.