Chung-Yih Sun

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.

A new GaAs sawtooth‐doping‐superlatticed switching device

A GaAs switching device with a double sawtooth‐doping‐superlattice (SDS) structure has been fabricated and demonstrated. By using the Kronig–Penny model, the dispersion relations of the electrons and holes in the zigzag quantum well were investigated. Two different delta‐doping sheets, 1 × 1012 and 1 × 1013 cm−2, were used in the double SDS structure. The period length of the SDS was 600 A. Thus, due to the sufficient barrier height and width, the calculated transmission coefficient of electrons was negligible when the studied structure was at thermal equilibrium or under a small‐biased condition. However, when a larger bias was applied, the studied structure exhibited an interesting negative‐differential‐resistance (NDR) performance in the experimental current‐voltage characteristics. This was caused by an avalanche multiplication process and the potential redistribution in SDS periods. Particularly, an interesting intermediate state between the initial off state and final on state was observed at 77 K. ...

A novel, very high breakdown voltage, field effect transistor prepared by molecular beam epitaxy

Abstract A novel, very high breakdown voltage, field effect transistor (FET) using a camel diode structure instead of a Schottky barrier gate has been fabricated successfully by molecular beam epitaxy. The camel diode gate has several advantages over a conventional metal-electron-semiconductor FET, including elimination of metallurgical difficulties of the metal-semiconductor contact, relatively easy adjustment of built-in voltage and the potential for improving reliability in adverse environments and under high power dissipation. If the gate length is reduced to 1 microm, a transconductance in excess of 200 mS mm −1 can be expected. A significant improvement of the gate-drain breakdown voltage to 70 V has been obtained. This excellent value is superior to those reported for other GaAs FETs. Consequently, the proposed structure is suitable for high power applications.

Regenerative switching properties of a sawtooth‐doping‐superlattice‐collector bipolar transistor

A molecular beam epitaxially grown GaAs three‐terminal switching device with controllable S‐shaped negative differential resistance (NDR) and switching voltages has been fabricated and demonstrated. The current‐voltage and switching characteristics of this device are excellent and reproducible. The switching voltage VS=9.6 V and holding voltage VH=5.1 V are obtained under two‐terminal operation. If a base current IB is applied, this device exhibits a controllable S‐shaped NDR phenomena both at the forward and reverse IB conditions. A bipolar transistor behavior with a current gain of over 20 is further achieved when the forward IB is employed. The proposed device having good potential for high speed and switching circuit applications has been shown by the results.

Application of Doping-Superlattice Collector Structure for GaAs Bipolar Transistor

In this paper, the GaAs sawtooth-doping-superlattice (SDS) collector has been respectively employed in homojunction and heterostructure transistors by molecular beam epitaxy (MBE). For both studied structures, conventional transistor behaviors and the controllable S-shaped negative-differential-resistance (NDR) performance were achieved at room temperature, simultaneously. In the normal- and inverted-mode two-terminal operations, the homojunction transistor exhibited a bi-directional switching phenomenon due to the avalanche multiplications within SDS periods or emitter-base junction depletion region. In addition, for the three-terminal operations, the common-emitter current gain of about 20 and a controllable S-shaped NDR family in larger current regime were obtained when a base current IB was applied. In this device, the base-controlled sensitivity SB was up to 8×10-3 V/µA. On the other hand, the heterostructure transistor was fabricated to improve the frequency response. In comparison with the prior structure, the heterostructure transistor performed similar current-voltage (I-V) characteristics, but a preferable current gain (up to 25) and base-controlled sensitivity SB (up to 1.6×10-1 V/µA) were obtained.

Investigation of GaAs Doping Superlattice Structure

The doping superlattice (DS) concept requires, however, that (i) a considerable potential modulation is achieved on a (ii) short length scale. The Moping technique is well suited to achieve such a considerabIe potential modulation on a short length scale, since delta doping allows us to accomplish (i) high doping concentration (>lo13 cm-2) and a (ii) localization of impurities on a length scale of the superlattice constant. Thus, these properties of the Moping technique made possible the growth and characterization of the Esaki-Tsu type doping superlattice. Here, we pay a great attention to the long period DS structure, in which an interesting S-shaped negative-differential-resistance (NDR) phenomenon resulting from the avalanche multiplications within superlattice periods was obtained . The append outline in Fig.1 shows the band profile of a double-period DS structure. A linear-potential approximation is used to described the zigzag potential barriers in the DS region. Solving the Schrddinger equation : where h is the reducedPla&ks constant and the effect mass m* is equated in dl potential regions. We get the wave function in the zero-potentid region with n = I and VI, where k=~~/h, and C, and D, are the constant coefficients of the wave function in nth period, respectively. However, in the DS region, with a proper coordinate transformation, the wave function can be described by using the Airy functions Ai(z) and Bi(z), @n(z) = C,eikz + Dne-ikz (2)

GaAs Bipolar Transistor with a Triple-Well Emitter Structure

In this paper, we start with the calculation on subbands of the undoped AlGaAs-GaAs triple-well structure by using transfer matrix approach. In order to obtain more accurate solutions, we have considered the influence of the different electron mass within quantum well8 and potential barriers. -The studied stgucture consists of a n+-GaAs, a 30-4 GaAs, a 204 Alo.Q and, subband E20 resonates with subband El0 when V, of 400mV is applied. The transmission resonance spectra (T*T-E,) for 80mV and 400mV external bias are shown in Fig.2(b) and We have also fabricated a GaAs bipolar transistor with a triple-well structure as emitter by molecular beam epitaxy (MBE). The current-voltage characteristics at 140K are shown in Fig.3. Only a negative-differential-resistance (NDR) phenomenon is observed. This is perhaps produced by the large energy difference existing between E20 and El*. The large number of the thermionic electrons, resulted from the higher external electric field, give a significant injection current and lead to a negligible resonant-tunneling effect in the transport properties. With a suitable parameter adjustment, this transistor will be more attractive in the design of quantum-functional devices. (c>*

Modeling and Simulating the Electrical Properties of Heterostructure-Emitter Bipolar Transistors

I. Introduction We develop a theoretical model related to minority carrier roperties to study the current ains of heterostructure-emitter bipolar transistors (HEBTsP which use an AlGaAs conventional single heterojunction bipolar transistor (HBT). In this study, minority carrier properties were described by means of polYpominal fit to the previous data. Here, the band-gap shrinkage in heavily doped layers was also taken into account. Current gains of 55 and 180 which are in agreement with calculated data were elyerimentally obtained for HEBTs with Alo.sGao.7As and Alo.sGa+sAs confinement layerst respectively. With the reduction of the base width to 0.1 pm, a current gain of around 1000 was expected. II. Theoretical Model An HEBT whose band diagram is shown in Fig.1 is a heterojunction bipolar transistor that has a homojunction emitter with a heterojuoction confinement layer on the top. The homojunctjon controls the electron injection while holes injected from the base are mostly reflected by the wide-gap confinement layer before they cm recombine with electrons. For simplicity, we assume that the hole recombination in the neutral emitter region is very small, and the dominant transport mechanisms are diffusion at the emitter homojunction and thermionic emission at the cod-nement heterojunction. Accordingly, the hole current injected from the pbase to the emitter contact can be expressed as layer o 3 y for minority carrier confinement to eliminate the problems associated with a