Der-Feng Guo

High-performance InGaP/GaAs pnp δ-doped heterojunction bipolar transistor

In this article, a novel InGaP/GaAs pnp δ-doped heterojunction bipolar transistor is first demonstrated. Though the valence band discontinuity at InGaP/GaAs heterojunction is relatively large, the addition of a δ-doped sheet between two spacer layers at the emitter-base (E-B) junction effectively eliminates the potential spike and increases the confined barrier for electrons, simultaneously. Experimentally, a high current gain of 25 and a relatively low E-B offset voltage of 60 mV are achieved. The offset voltage is much smaller than the conventional InGaP/GaAs pnp HBT. The proposed device could be used for linear amplifiers and low-power complementary integrated circuit applications.

Surface treatment effect on temperature-dependent properties of InGaP∕GaAs heterobipolar transistors

Specific treatments of the base surface of InGaP∕GaAs heterojunction bipolar transistors are studied experimentally. The dual treatment method, based on the combination of ledge and sulfur passivation, shows better temperature-dependent characteristics including higher dc gain, lower saturation voltage, lower base-emitter junction turn on voltage, lower leakage current, lower collector and base current ideality factors nC and nB, and wider collector current operating regimes over the measured temperature range (300–400K). Therefore, the dual surface treatment method provides promise for high-performance electronic applications.

Improved Current-Spreading Performance of an InGaN-based Light-Emitting Diode with a Clear P-GaN/N-GaN Barrier Junction

The InGaN-based light-emitting diode (LED) with a clear p-GaN/n-GaN barrier junction is fabricated and investigated. Due to the built-in potential induced by this junction, superior current spreading performance is achieved. In addition, the suppression of current crowding phenomenon yields the reduced parasitic effect. Therefore, under an injection current of 20 mA, improved behaviors including lower turn-on voltage, lower parasitic series resistance, and significantly enhanced electrostatic discharge (ESD) performance are presented.

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.

Investigation of the Electrostatic Discharge Performance of GaN-Based Light-Emitting Diodes With Naturally Textured p-GaN Contact Layers Grown on Miscut Sapphire Substrates

The electrostatic discharge (ESD) characteristics of GaN-based light-emitting diodes (LEDs) with naturally textured p-GaN contact layers grown on c-axis miscut sapphire substrates are studied and demonstrated. Based on the machine model, the device grown on a 0.35° miscut sapphire shows the highest ESD tolerance, whereas the device grown on a 0.2° miscut sapphire exhibits the poorest tolerance. It is found that this phenomenon is primarily related to the presence of maximum capacitance Cm values rather than the difference in defect densities between LEDs. The variation in Cm values is caused by the parasitic capacitance effect induced by different p-GaN surface morphologies between the studied devices. This observation gives us a more reliable application in improving the ESD performance based on the device grown on a 0.35° miscut sapphire.

Temperature dependences of an In0.46Ga0.54As/In0.42Al0.58As based metamorphic high electron mobility transistor (MHEMT)

In this paper, an interesting thermally stable In0.42Al0.58As/In0.46Ga0.54As metamorphic high electron mobility transistor (MHEMT) is fabricated and investigated. Good dc and RF characteristics are obtained by precisely depositing gold (Au) upon the In0.42Al0.58As barrier layer as the Schottky contact metal. For a MHEMT with gate dimensions of 1 × 100 µm2, high gate–drain breakdown voltage, high turn-on voltage, low gate leakage current density, high maximum transconductance with broad operating regime and low output conductance are obtained even at ambient temperatures up to 510 K (240 °C). The studied device also shows a very good microwave performance at room temperature. Moreover, the relatively low variations of the device performance are achieved over a wide temperature range (from 300 to 510 K). Therefore, the studied device has a good thermally stable performance that is suitable for high-speed and high-power electronic applications.

Investigation of Amplifying and Switching Characteristics in Double Heterostructure-Emitter Bipolar Transistors

Double heterostructure-emitter bipolar transistors (DHEBTs) with emitter edge-thinning design and DHEBTs without that design have been investigated. In the characteristics modeling, a two-dimensional continuity equation and boundary conditions in the base region are employed to determine the various components of base current in a cylindrical mesa-type DHEBT. The influence of structure parameters and emitter edge-thinning design on the current gain of the DHEBT is studied. The effect of quasi-electric field in the base region is taken into account. Switching mechanisms in the DHEBT are also discussed. In the experimental measurement, a DHEBT with an exposed p + -GaAs base surface exhibits a small offset voltage of 100 mV and a common-emitter current gain of 17. Due to the emitter edge-thinning to suppress the surface recombination current, a DHEBT with an N-AlGaAs passivated surface has a common-emitter current gain of 140 and a negligible offset voltage of 40 mV. With symmetric structures, both devices present bidirectional switching phenomena. Moreover, the emitter edge-thinning design is found having the capability for reducing the holding power in the switching. Possessing both amplifying and switching features, the DHEBTs show good potentials for circuit applications.

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. >

Temperature Effect of a Heterojunction Bipolar Transistor with an Emitter-Edge-Thinning Structure

The temperature-dependent characteristics of an InGaP/GaAs heterojunction bipolar transistor (HBT) with an emitter-edge-thinning structure are studied and demonstrated. Based on the use of the emitter-edge-thinning structure, higher current gain and lower base surface-recombination current density over the measured temperature range (300-400 K) are obtained. In addition, the device shows the improved thermal stability on dc current gain performance. Therefore, the studied HBT device with an emitter-edge-thinning structure has promise for low-power and higher temperature electronic applications.

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.