Rong-Chau Liu

Investigation of temperature-dependent characteristics of an n/sup +/-InGaAs/n-GaAs composite doped channel HFET

The temperature-dependent characteristics of an n+-InGaAs/n-GaAs composite doped channel (CDC) heterostructure field-effect transistor (HFET) have been studied. Due to the reduction of leakage current and good carrier confinement in the n+-InGaAs/n-GaAs CDC structure, the degradation of device performances with increasing the temperature is insignificant. Experimentally, for a 1 x 100 μm2 device, the gate-drain breakdown voltage of 24.5 (22.0) V, turn-on voltage of 2.05 (1.70) V, off-state drain-source breakdown voltage of 24.4 (18.7) V, transconductance of 161 (138) mS/mm, output conductance of 0.60 (0.60) mS/mm, and voltage gain of 268 (230) are obtained at 300 (450) K, respectively. The shift of Vth from 300 to 450 K is only 13 mV. In addition, the studied device also shows good microwave performances with flat and wide operation regime.

Influences of surface sulfur treatments on the temperature-dependent characteristics of HBTs

The temperature-dependent DC characteristics of InGaP-GaAs heterojunction bipolar transistors with and without sulfur treatment are systematically studied and demonstrated. Due to the use of sulfur passivation, the series resistance of base-emitter junction of studied device can be effectively reduced. In addition, the device with sulfur treatment can be operated under ultra low collector current regimes (I/sub C//spl les/10/sup -11/ A). Experimentally, a long-time sulfur treatment is not appropriate. In this work, the studied device with sulfur treatment for 15 min is a good choice. Furthermore, at measured temperature (298 K-398 K), the studied device with sulfur treatment can reduce collector-emitter offset voltage and the impact of emitter size effect. Moreover, as the temperature is increased, the device with sulfur treatment will exhibit higher DC current gain and more stable temperature-dependent performances. This will extend the application regimes of the studied device in low-power and communication systems.

Pd-oxide- Al/sub 0.24/Ga/sub 0.76/As (MOS) high electron mobility transistor (HEMT)-based hydrogen sensor

An interesting hydrogen sensor based on an Al/sub 0.24/Ga/sub 0.76/As Schottky barrier high-electron mobility transistor with a catalytic Pd metal/oxide/semiconductor is fabricated and demonstrated. In comparison with traditional Schottky diodes or capacitance-voltage type hydrogen sensors, the studied device exhibits larger current variation, lower hydrogen detection limit, and shorter transient hydrogen response time. Besides, good hydrogen-sensing properties, such as significant drain current change, threshold voltage shift, and transconductance change of transistor behaviors, are obtained. Therefore, the studied device provides the promise for high-performance solid-state hydrogen sensors, optoelectronic integrated circuits, and microelectromechanical system applications.

DC characterization of an InP-InGaAs tunneling emitter bipolar transistor (TEBT)

The dc performances of a novel InP-InGaAs tunneling emitter bipolar transistor (TEBT) are studied and demonstrated. The studied device can be operated under an extremely wide collector current regime larger than 11 decades in magnitude (10/sup -12/ to 10/sup -1/ A). A current gain of 3 is obtained even operated at an ultralow collector current of 3.9/spl times/10/sup -12/ A (1.56 /spl times/10/sup -7/ A/cm/sup 2/). The common-emitter and common-base breakdown voltages of the studied device are higher than 2 and 5 V, respectively. Furthermore, a very low collector-emitter offset voltage of 40 mV is found. The temperature-dependent dc characteristics of the TEBT are measured and studied. Consequentially, based on experimental results, the studied device provides the promise for low-power electronics applications.

Comprehensive investigation on emitter ledge length of InGaP∕GaAs heterojunction bipolar transistors

The influence of emitter ledge length on the performance of InGaP∕GaAs heterojunction bipolar transistors is comprehensively investigated. Due to the band-bending effect at the intersection of the emitter ledge edge with the exposed base surface, an undesired potential saddle point is formed. Moreover, emitter ledge passivations that are longer or shorter than an optimal length result in the deterioration of device performance. Based on the theoretical analysis and experimental results, the surface recombination effect of the device with an emitter ledge length of 0.8μm is negligible compared with the unpassivated device. Also, the device with the emitter ledge length of 0.8μm shows nearly the best dc characteristics and acceptable rf performance. Therefore, the optimum emitter ledge length in this study is near 0.8μm.

Characteristics of metal-insulated-semiconductor (MIS) like In0.2Ga0.8AsGaAs doped-channel structure

Abstract A metal-insulated-semiconductor (MIS) like In 0.2 Ga 0.8 As GaAs doped-channel structure has been proposed. Furthermore, a field-effect transistor (FET) based on the proposed structure is also fabricated. Both theoretical simulations and experiments are made and compared in this paper. First, the theoretical analysis by using the self-consistent method with a quadratic expression of the charge control process is employed to simulate the basic electronic properties of the doped-channel FET. From the simulation results, we can find that the d.c. performances show good transistor characteristics. For the experimental results, a high breakdown voltage of 17.4 V, a maximum drain saturation current of 930 mA/mm, a maximum transconductance of 235 mS/mm, and a very broad gate voltage range larger than 3 V with the transconductance higher than 200 mS/mm are obtained for a 2 × 100 μm2 gate-dimension FET. From the comparison, we find that experiment results are in a good agreement with the theoretical simulations. The performances provide a promise of the proposed device to be a good candidate for practical circuit applications.

Comprehensive Study of Thermal Stability Performance of Metamorphic Heterostructure Field-Effect Transistors with Ti ∕ Au and Au Metal Gates

The thermal stability performance of double 8-doped In 0.42 Al 0.58 As/In 0.46 Ga 0.54 As metamorphic heterostructure field-effect transistors with Au and Ti/Au metal gates are comprehensively studied and demonstrated. By evaporating the Ti/Au metal gate, the thermal stability of device characteristics are significantly improved as compared with the device with conventional metal gate (Au). Experimentally, the device with a Ti/Au metal gate simultaneously exhibits the considerably lower temperature degradation in turn-on voltage (-2.19 mV/K), breakdown voltage (-34 mV/K), logic swing (-1.24 mV/K), transition region width (0.05 mV/K), on-off current ratio (-3.55 /K), threshold voltage (-0.25 mV/K), impact ionization-induced gate current (1.63 X 10 -3 μA/mm K), output conductance (1.23 μS/mm K), and voltage gain (-0.33 /K) as the temperature is increased from 300 to 510 K. Consequently, the studied device with a Ti/Au metal gate is a good candidate for high-speed and high-temperature digital and switching circuit applications.

The Effect of Sulfur Treatment on the Temperature-Dependent Performance of InGaP/GaAs HBTs

Temperature-dependent dc characteristics and RF performances of InGaP/GaAs heterojunction bipolar transistors with sulfur treatment are systematically studied. The base-surface-recombination current, specific contact resistance, and sheet resistance of the studied devices can be effectively reduced by sulfur treatment. Practically, long-time sulfur treatment is not appropriate. In this paper, the studied device with the sulfur treatment for 12-15 min is a good choice. Experimentally, the collector-emitter offset voltage DeltaVCE and dc current gain with sulfur treatment can be substantially reduced and increased, respectively, over the 300-K-400-K temperature range. Moreover, as the temperature is increased, the device with sulfur treatment exhibits temperature-independent or thermally stable performances. The devices with sulfur treatment also exhibit improved RF characteristics

Characterization of InP/InGaAs double-heterojunction bipolar transistors with tunnelling barriers and composite collector structures

We study and demonstrate the dc performance of two InP/InGaAs double-heterojunction bipolar transistor (DHBTs) with the undoped tunnelling barrier and composite collector structures. Due to the mass filtering effect for holes, a thin InP tunnelling barrier can be used to replace the wide-gap emitter. By varying the thickness of the barrier, distinct collector current ideality factors can be obtained which reveal different injection mechanisms at the emitter. The 4000 A InP collectors with InP/InGaAs abrupt junctions and InP/InGaAsP/InGaAs step-graded junctions achieve high breakdown voltages of 9.2 and 14.6 V, respectively. Furthermore, the abrupt junction and δ-doping structure eliminate carrier blocking across the base-collector heterojunction more effectively than the step-graded junction. We find that the reduction of the multiplication avalanche of the step-graded junction DHBT leads to the severe self-heating effect. For the abrupt junction DHBT, the dc current gain is almost independent of the perimeter-to-area ratio of the emitter due to the low surface recombination.

Influence of Emitter-Edge-Thinning Thickness on the Heterojunction Bipolar Transistor Performance

In this work, the characteristics of the InGaP/GaAs heterojunction bipolar transistors with different emitter-edge-thinning thickness were systematically investigated. A stronger downward-band-bending phenomenon was observed at the edge of emitter-edge-thinning intersection with the exposed base surface. This band bending induced the presence of a potential saddle point, which substantially increased the recombination rates and electron densities. In addition, the decision of emitter-edge-thinning thickness plays a key role in reducing surface recombination at the potential saddle point. As the emitter-edge-thinning thickness was selected between 100 and 200 A, the lowest recombination rate and electron density and highest dc current gain could be obtained. Furthermore, good agreements between the theoretical analyses and experimental results were found.