Wen-Shiung Lour

AlGaAs/GaAs heterostructure-emitter bipolar transistor (HEBT) prepared by molecular beam epitaxy

Abstract A novel AlGaAs/GaAs heterostructure-emitter bipolar transistor (HEBT) has been fabricated and demonstrated. The problems of conventional single heterojunction bipolar transistors (SHBTs) such as graded AlxGa1-xAx emitter and the precise alignment of emitter-base junction are avoided. The proposed HEBT device exhibits significant advantages as (i) ease of fabrication, (ii) extremely small collector offset voltage. The common-emmiter current gain up to 180 with an offset voltage about 80 mV has been obtained in the nonoptimized device. Furthermore, an interesting controllable S-shaped negative-differential-resistance (NDR) phenomenon is observed under reverse operation mode. Therefore, the proposed HEBT may be employed as a multiple-function device which provides the transistor and switch actions on the same wafer, simultaneously.

Influence of the potential spike on heterostructure‐emitter bipolar transistor

The influence of potential spike on the transport properties of heterostructure‐emitter bipolar transistor (HEBT) has been demonstrated. The potential spike is attributed primarily to the extended depletion region adjacent the p+ GaAs base layer. Due to the existence of potential spike, the electrical properties including conducting current, current gain, and offset voltage, etc., are degraded seriously. The knee‐shaped characteristics and strong reachthrough effect are observed. Consequently, the design of the structural parameters, such as GaAs emitter (collector) width adjacent p+ base, plays an important role of high‐performance HEBT devices.

A new functional, resonant‐tunneling bipolar transistor with a superlattice emitter

We report a new resonant‐tunneling bipolar transistor (RBT), in which electrons are injected from emitter to base by resonant‐tunneling through the minibands in the i‐AlGaAs/n+‐GaAs superlattice emitter. The main feature of the device is the significant double negative‐differential‐resistance both at room temperature and low temperature. Two high peak‐to‐valley (PV) current ratios of 4:1 and 2.6:1 were obtained at 77 K. In the common emitter configuration, bistable output currents exist as controlled by the base‐emitter voltage at critical values of VBE = 2.5u2009V and VBE = 3u2009V, respectively. In addition, two negative transconductance operation regions were obtained when the base‐emitter voltage was applied. Yet, three different transistor action regions occur as the control base current is being applied. For base currents that are not high enough to bring the base‐emitter junction to flat‐band condition, common‐emitter current gain up to 65 was obtained. This is the highest value ever reported in an RBT dev...

New AlGaAs/GaAs double heterostructure‐emitter bipolar transistor prepared by molecular beam epitaxy

A new AlGaAs/GaAs double heterostructure‐emitter bipolar transistor (DHEBT) prepared by molecular beam epitaxy (MBE) has been demonstrated. Due to the symmetric structure with respect to the base layer, the device would operate as a bi‐directional transistor and switch. The common‐emitter current gain for up to 18, with an offset voltage smaller than 0.1 V, is obtained. Furthermore, the undesired knee‐shaped characteristics and the reachthrough effect observed in the conventional double heterojunction bipolar transistor (DHBT) are avoided. The bi‐directional operations of this structure give a significant flexibility in the circuit applications. It is believed that with adequate adjustments on structural parameters, especially in the minimization of the base‐collector junction area, a more symmetric and an improved electrical performance may be achieved.

AlGaAs/GaAs double-heterostructure-emitter bipolar transistor (DHEBT)

An AlGaAs/GaAs double-heterostructure-emitter bipolar transistor (DHEBT) fabricated by molecular beam epitaxy (MBE) is presented. The use of a structure symmetrical with respect to the base layer results in bidirectional transistor and switching behavior. Due to a significant area difference between emitter-base and base-collector junction, an asymmetrical property is observed. With an emitter edge-thinning design, the transistor performance may be further improved. A common-emitter current gain of up to 140 with a negligible collector-emitter offset voltage ( approximately 40 mV) is achieved. A bidirectional S-shaped negative-differential-resistance (NDA) phenomenon occurs at high V/sub CE/ bias voltage. The temperature dependence of the NDR is investigated. A three-terminal-controlled switching device is found to perform well when the control current is introduced into the base electrode. >

Power MISFETs fabricated with superlatticed gate “insulators” and transition buffer layers

Abstract A new GaAs MISFET with superlatticed gate “insulator” and transition buffer layer structure is proposed in this paper. The use of an undoped GaAsue5f8Al0.3Ga0.7As superlatticed gate “insulator” provides a high gate breakdown voltage ( > 36 V) with very low prebreakdown leakage current and a low gate capacitance (Cgs), compared to usual MESFET devices. Due to the existence of the gate “insulator”, a high carrier concentration can be employed in the active channel, which improves the outer-drain-current capability and transconductance (over 200 mS/mm can be expected if the gate length is reduced to 1 μm). Also three different transition-buffer layers i.e. superlattice, graded superlattice and modulation-doped (MD) structures have been inserted between the active-channel and buffer layer respectively, to offer an excellent carrier confinement (to obtain a small interface degraded region) or to enhance the electrical performance of the active channel. Finally, the Iue5f8V characteristics, output conductance and transconductance gm of the superlatticed gate FETs with different transition-buffer layers are investigated and compared. From the experimental results, it is clear that the proposed structures are suitable for power application.

Application of an emitter edge‐thinning technique to GaAs/AlGaAs double heterostructure‐emitter bipolar transistor

A GaAs/AlGaAs double heterostructure‐emitter bipolar transistor (DHEBT), prepared by molecular beam epitaxy, has been fabricated with improved performance. The employment of emitter edge‐thinning technique has caused a significant suppression of the surface leakage current. A common‐emitter current gain of up to 140 with a negligible collector offset voltage (∼40 mV) was obtained. The undesired knee‐shaped characteristics and the reachthrough effect, always observed on the conventional double heterojunction bipolar transistor (DHBT), were eliminated. An interestingly bi‐directional and three‐terminal controlled switching phenomena may also be exhibited by this device. This gives a substantial flexibility in the device and circuit applications. The electrical performance is believed to be further improved with an adequate design to minimize the area difference between emitter‐base (EB) and the base‐collector (BC) junction.

Application of a triple‐well superlattice emitter structure to GaAs switching device

A new GaAs switching device with a triple‐well superlattice emitter structure, prepared by molecular beam epitaxy, has been fabricated and demonstrated. An S‐ and N‐shaped negative‐differential‐resistance (NDR) phenomenon, attributed primarily to the avalanche multiplications process and resonant‐tunneling effect, were observed simultaneously when a proper collector‐emitter voltage (VCE) was applied. The operation temperature is known from the experimental results to play an important role on the influence of the NDR behaviors. A transistor action with a common‐emitter current gain of over 36 was also achieved at 300 K when a control current was employed to the base electrode. This device exhibited a significantly regenerative switching phenomenon both at room temperature and low temperature if a −VCE voltage was used. The proposed structure consequently has good potential for switching and quantum functional device applications.

Morphological defects on Be-doped AlGaAs layers grown by MBE

Abstract The primary surface morphology, oval defects, of MBE-grown Be-doped AlGaAs layers has been studied using two different As partial pressure control methods, i.e., thermocouple (TC) and nude ion gauge (NIG) methods. The observed defect density has been studied as a systematic function of growth parameters, including doping concentration, substrate temperature, growth rate, epilayer thickness, and As partial pressure. The protrusion-induced oval defects were formed during MBE growth. The primary origin of the oval defects generated in our system is believed to be the presence of non-volatile III 2 O 3 oxide. However, an oval defect density less than 600 cm -2 has been obtained through optimization of the growth parameters, and after paying careful attention to substrate preparation and vacuum conditions.

A study on beryllium-doped AlxGa1 − xAs layers grown by molecular beam epitaxy

Abstract The characteristics of beryllium-doped Al x Ga 1 − x As grown by molecular beam epitaxy (MBE) have been studied in this paper. The primary surface morphology (oval defect) exhibits a strong dependence on source purity, substrate preparation, vacuum quality and growth conditions. In the studied experiments, an important criterion of substrate temperature, T s = 580 ° C , was found significant for MBE growth. The studied Al x Ga 1 − x As films were semi-insulating high resistance as long as the substrate temperature is lower than 580°C. The electrical and photoluminescent properties of the Al x Ga 1−x As layers were studied and showed a different dependence on the substrate temperature.