Lih-Wen Laih

Sequence influence of nonidentical InGaAsP quantum wells on broadband characteristics of semiconductor optical amplifiers--superluminescent diodes.

Extremely broadband emission is obtained from semiconductor optical amplifiers-superluminescent diodes with nonidentical quantum wells made of InGaAsP/InP materials. The well sequence is experimentally shown to have a significant influence on the emission spectra. With the three In(0.67) Ga(0.33) As(0.72) P(0.28) quantum wells near the n -cladding layer and the two In(0.53) Ga(0.47) As quantum wells near the p -cladding layer, all bounded by In(0.86) Ga(0.14) As(0.3)P(0.7) barriers, the emission spectrum could cover from less than 1.3 to nearly 1.55 microm, and the FWHM could be near 300 nm.

A novel InGaP/GaAs S-shaped negative-differential-resistance (NDR) switch for multiple-valued logic applications

In this paper, a novel InGaP/GaAs multiple S-shaped negative-differential-resistance (NDR) switch based on a heterostructure-emitter bipolar transistor (HEBT) structure is fabricated and demonstrated. An interesting multiple NDR phenomenon resulting from an avalanche multiplication and successive two-stage barrier lowering process is observed under the inverted operation mode. The three-terminal-controlled and temperature-dependent NDR characteristics are also investigated. In addition, a typical transistor performance is found under the normal operation mode. Consequently, owing to the presented different stable operation points and transistor action, the studied device shows a good potential for multiple-valued logic and analog amplification 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.

On the recombination currents effect of heterostructure-emitter bipolar transistors (HEBTs)

Abstract In this paper, we will demonstrate the effect of recombination current on the electrical properties of heterostructure-emitter bipolar transistors (HEBTs). For comparison, an AlGaAs/GaAs and an AlInAs/GaInAs HEBT are fabricated with the same layer structure. The theoretical analysis shows that the neutral-emitter recombination current in the neutral emitter regime is a significant factor for determining transistor characteristics. For the AlGaAs/GaAs HEBT, the hole diffusion length is larger than the emitter thickness, so that most of holes can be reflected back at the confinement layer due to the hole recombination current being low in the neuter-emitter region. Thus, the high emitter injection efficiency and current gain can be achieved simultaneously. On the other hand, for the AlInAs/GaInAs HEBT, the increase of recombination current at neutral emitter regime and the existence of potential spike could reduce the emitter injection efficiency at large VBE voltage. Hence, the non-1KT component of collector current is enhanced and the characteristics of transistor are degraded. However, a lower offset voltage of 40 mV is obtained attributed to the low base surface recombination current for the AlInAs/GaInAs HEBT. All of these experimental results are consistent with the theoretical analysis.

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.

Investigation of an InGaAsGaAs doped-channel MIS-like pseudomorphic transistor

Abstract A GaAsInGaAs doped-channel MIS-like pseudomorphic FET has been fabricated and investigated. The device under study shows advantages of high breakdown voltage, high current capability, very large gate voltage swing for high transconductance operations, and ease of fabrication. For a 2 × 100 μ m 2 gate device, a breakdown voltage of 17.4 V, a maximum drain saturation current of 930 mA/mm, a maximum transconductance of 230 mS/mm, and a very broad gate voltage range larger than 3 V with the transconductance higher than 200 mS/mm are obtained. An estimated electron saturation velocity v s up to 2.2 × 10 7 cm/s is acquired even for a thin InGaAs channel layer with a 4 × 10 18 cm −3 doping level. A simple two-layer model is also proposed to study the theoretical properties which shows a good agreement with the experimental results. Consequently, the device demonstrates a good potential for use in high-speed, high power and large input signal circuit applications.

High‐performance camel‐gate field effect transistor using high‐medium‐low doped structure

We report an improved camel‐gate field effect transistor using a high‐medium‐low doped channel. A 1000‐A‐thick n=1×1017 cm−3 GaAs layer is employed to form the camel gate, which prevents the planar‐doped barrier from being dropped abruptly. In addition to transition channel, a thin (200 A) heavily doped (n=5×1017 cm−3) GaAs layer works as the main active channel to enhance the current drivability and transconductance. For our 1.5×100 μm2 device, the maximum current density of over 850 mA/mm was obtained. Moreover, an enhanced voltage‐independent transconductance was also observed. Generally, the device exhibits a transconductance of 220 mS/mm which is compatible to that of MESFETs and is two‐ or threefold to that of reported camel‐gate FETs. In addition, the proposed device demonstrates a large gate voltage swing for high transconductance operation. Due to the excellent device performance, our devices do hold promise for both large signal and digital circuits application, simultaneously.

On the multiple negative-differential-resistance (MNDR) InGaP-GaAs resonant tunneling bipolar transistors

Two InGaP/GaAs resonant tunneling bipolar transistors (RTBTs) with different superlattice (SL) structures in the emitters are fabricated and studied. The uniform and modulated widths of barriers are respectively utilized in the specific SL structures. Based on the calculations, the ground state and first excited state minibands are estimated from the transmission probability. The electron transport of RT through SL structures is significantly determined by the electric field behaviors across the barriers. Experimentally, the excellent transistor characteristics including the small saturation voltage, small offset voltage and high breakdown voltages are obtained due to the insertion of /spl delta/-doping sheet at the base-collector (B-C) heterointerface. Furthermore, at higher current regimes, the double- and quaternary-negative difference resistance (NDR) phenomena are observed in agreement with the theoretical prediction at 300 K.

Multiple-route current-voltage (I-V) characteristics of GaAs-InGaAs metal-insulator-semiconductor-like (MIS) structure for multiple-valued logic applications

A new GaAs-In/sub x/Ga/sub 1-x/As metal-insulator-semiconductor-like (MIS) device with the interesting dual-route and multiple-negative-differential-resistance (MNDR) current-voltage (I-V) characteristics has been fabricated and demonstrated. These performances are caused by the successive barrier lowering and potential redistribution effect. A novel multiple-route I-V characteristic is obtained in the studied device at low temperature (-130/spl deg/C). This performance is different from the previously reported NDR switching device and has not yet been found in other devices. The interesting property of the studied structure provides a promising candidate for switching device applications.

1.3-/spl mu/m n-type modulation-doped AlGaInAs/AlGaInAs strain-compensated multiple-quantum-well laser diodes

In this paper, we report the fabrication and characterization of 1.3-/spl mu/m AlGaInAs/AlGaInAs laser diodes (LDs) with an n-type modulation-doped strain-compensated multiple-quantum-well (MD-SC-MQW) active region and a linearly graded index separate confinement heterostructure. The barrier in the MD-SC-MQW active region contains the 28 /spl Aring/ Si-doped modulation-doped region and two 29 /spl Aring/ surrounding undoped regions that serve to prevent the overflow of Si doping atoms into the wells. We investigate the threshold current density, infinite current density, differential quantum efficiency, internal quantum efficiency, internal optical loss, threshold gain (for the cavity length of 300 /spl mu/m), and transparency current density as a function of doping concentration in the n-type AlGaInAs barrier for the 1.3-/spl mu/m MD-SC-MQW LDs. The theoretical and experimental results show that the optimum doping concentration of doped barriers is 5/spl times/10/sup 18/ cm/sup -3/. With this optimum condition, the 3.5-/spl mu/m ridge-striped LDs without facet coating will exhibit a lower threshold current and a higher differential quantum efficiency of 18 mA and 52.3% under the CW operation as compared to those of 22 mA and 43% for the undoped active region, respectively. In addition, a high characteristic temperature of 70 K, a low slope efficiency drop of -1.3 dB between 20 and 70/spl deg/C, and a wavelength swing of 0.4 nm//spl deg/C for the LDs operated at 60 mA and 8 mW can be obtained in the LDs with doped barriers.