Double Heterojunction Research Articles

A comparative study on electroluminescence from ZnO-based double heterojunction light emitting diodes grown on different lattice mismatch substrates

We have comparatively investigated the electroluminescence (EL) performance from the asymmetric p-Mg0.05Zn0.95O/i-ZnO/n+-GaN and p-Mg0.05Zn0.95O/i-ZnO/n+-Si double-heterojunction light emitting diodes (LEDs) grown on different lattice mismatch substrates. The I–V curve measurements show clear rectification characteristics with a threshold voltage of 3.8 and 6V for the p-Mg0.05Zn0.95O/i-ZnO/n+-GaN and p-Mg0.05Zn0.95O/i-ZnO/n+-Si double heterojunctions, respectively. A strong violet-ultraviolet EL emission and no deep-level emission were observed for the p-Mg0.05Zn0.95O/i-ZnO/n+-GaN double heterojunction grown on small lattice-mismatched n+-GaN substrate. In comparison, a dominant visible emission band and a weak ultraviolet emission peak were observed for p-Mg0.05Zn0.95O/i-ZnO/n+-Si double heterojunction grown on large lattice-mismatched n+-Si substrate. The difference between both LEDs is due to different quality of the MgZnO and ZnO layers grown on different lattice mismatch substrates.

Bipolar characteristics of AlGaN/AlN/GaN/AlGaN double heterojunction structure with AlGaN as buffer layer

Abstract This is a theoretical study of AlGaN/AlN/GaN/AlGaN double heterojunction (DH) structure with AlGaN as buffer layer. Our calculation shows that as the buffer Al content increases, though two-dimensional electron gas (2DEG) sheet density decreases, the channel back-barrier caused by polarization-induced electric field in GaN provides better electron confinement. And under certain conditions the DH-structure shows bipolar characteristics, with an additional two-dimensional hole gas (2DHG) formed at GaN/AlGaN interface. The influence of the buffer Al content and GaN channel thickness on the 2DEG and 2DHG sheet densities are investigated, and the conditions for the disappearance of 2DHG are discussed. Also, the mobility inhibited by dislocation scattering is enhanced in DH-structure due to the enhancement of screening effect of the 2DEG.

AlGaAs anode heterojunction PIN diodes

AbstractThis paper describes the development of a heterojunction AlGaAs/GaAs PIN diode as a revolutionary improvement as compared to the homojunction GaAs PIN diode commonly used in microwave systems for commercial and military applications. In a heterojunction device the injected carriers from the junction are confined by the bandgap discontinuity between the AlGaAs/GaAs layers. This confinement effectively reduces the series resistance within the I‐region of a PIN diode. Simulations of both single and double heterojunction PIN diodes predict a significant improvement in the return loss and insertion loss as compared to an equivalent GaAs PIN structure. In particular, the single heterojunction PIN diode, when simulated at a bias of 10 mA, indicates a factor of two reduction in high frequency insertion loss. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dielectric and barrier thickness fluctuation scattering in Al2O3/AlGaN/GaN double heterojunction high-electron mobility transistors

The two-dimensional electron gas (2DEG) mobility limited by dielectric and barrier thickness fluctuations (TF) scattering in Al2O3/AlGaN/GaN double heterojunction high-electron mobility transistors (HEMTs) is calculated. Calculation shows that thickness fluctuation scattering is the main limitation in Al2O3/AlGaN/GaN double heterojunction HEMTs with thin Al2O3 layer thicknesses. In addition, a study of 2DEG mobility as a function of 2DEG density, ns, shows that TF scattering acts as the main limitation when ns exceeds 2×1012cm−2. The results may be used to design HEMTs to obtain higher 2DEG mobilities by modulating the dielectric layer and barrier thicknesses or 2DEG density.

Millimeter‐wave INP DHBT power amplifier based on power‐optimized cascode configuration

AbstractThis letter describes the use of a power‐optimized cascode configuration for obtaining maximum output power at millimeter‐wave (mm‐wave) frequencies for a two‐way combined power amplifier (PA). The PA has been fabricated in a high‐speed InP double heterojunction bipolar transistor technology and has a total active emitter area of 68.4 μm2. The experimental results demonstrate a small signal gain of 9.8 dB and saturated output power of more than 18.6 dBm at 72 GHz with a peak power‐added efficiency of 12%. The benefits of the power optimized cascode configuration over the standard cascode configuration at mm‐wave frequencies are confirmed by both simulations and experimental results. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1178–1182, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27477

70 GSa/s and 51 GHz bandwidth track‐and‐hold amplifier in InP DHBT process

A differential 70 GSa/s track-and-hold amplifier has been designed and fabricated in a 320 GHz-f T InP double heterojunction bipolar transistor process. Measurements show a 51 GHz small-signal bandwidth with an S 11 parameter lower than -15 dB up to 56 GHz. The transient operation is verified up to 70 GSa/s. 60 GSa/s spectral measurements give total harmonic distortion ←46 dB up to 7 GHz and ←37 dB over the whole measurement range.

An improved model for InP/InGaAs double heterojunction bipolar transistors

An improved VBIC model for InP/InGaAs double heterojunction bipolar transistors (DHBTs) is proposed. The model accounts for the double heterojunction effect and current blocking effect with novel current expressions. New empirical formulas for the collector-base capacitance and transit time are developed to explain the mobile-charge modulation effect and the role of negative differential mobility. DC and S-parameter measurements are conducted in order to realize the whole extraction flow. The accuracy and validity of this new model and extraction strategy are demonstrated by comparisons of simulation to measurement data on DC, AC small-signal and large-signal characteristics over a wide bias region.

Negative differential photovoltage in a biased double heterojunction

We report on negative differential photovoltage (DPV), which is observed under modulated photoexcitation of a double heterojunction, when the common positive photovoltage increment due to photocurrent modulation is suppressed by high bias current. The negative DPV was shown to be due to the effect of photoconductivity on the series resistance of the heterojunction and due to the modulation of junction temperature. In AlGaInP double heterojunction light-emitting diodes, the magnitudes of negative DPV in the range of −10 μV correspond to the estimated variation of series resistance and junction temperature as low as ∼10−3 Ω and ∼10−2 K, respectively.

Effect of Various Structures on the Efficiency of Organic Solar Cells

Small molecule organic solar cell with an optimized structure of indium tin oxide (ITO)/copper phthalocyanine (CuPc) (10nm)/CuPc: C60mixed (20nm)/fullerene (C60) (20nm)/bathocuproine (BCP) (10nm)/Al) was fabricated. With optimizing the hybrid planar-mixed molecular heterojunction (PM-HJ) from the double layer heterojunction (HJ) and the bulk heterojunction (BHJ), the short-circuit current density (Jsc) increased from 3.09 to 5.11mA/cm2, the open-circuit voltage (Voc) increased from 0.40 to 0.47V, and the power conversion efficiency (ηp) increased from 0.66 to 1.28% under 100mW/cm2 AM1.5G illumination. These improvements were attributed to reach the optimal balance among the light absorption efficiency, the exciton dissociation efficiency and the carrier collection efficiency of the device, resulting in enhancement of Jscwithout affecting the value of fill factor (FF) and the reduction of the dark current. Furthermore a decrease of dark current is caused to the higher Voc.

A 38 TO 44 GHZ SUB-HARMONIC BALANCED HBT MIXER WITH INTEGRATED MINIATURE SPIRAL TYPE MARCHAND BALUN

This work presents an active balanced sub-harmonic mixer (SHM) using InP double heterojunction bipolar transistor technology (DHBT) for Q-band applications. A miniature spiral type Marchand balun with five added capacitances for improved control of amplitude and phase balance is integrated with the SHM. The measured results for the SHM demonstrates a conversion gain of 1.2 dB at an RF frequency of 41 GHz with an associated LO power of 5 dBm. The conversion loss remains better than 3 dB from 38 to 44 GHz. The LO to IF isolation is better than 42 dB within the bandwidth of the mixer and confirms the excellent balance of the integrated spiral type Marchand balun. The DC power consumption of the SHM is only 22.5mW under normal mixer operation.

Analytical Surface Charge Control Model for AlN/GaN/AlGaN Double Heterojunction Field-Effect Transistor

We have argued that the nature of surface potential variation with gate voltage of AlN/GaN/AlGaN Double Heterojunction Field Effect Transistor (DHFET) is no different from that of the conventional GaAs/AlGaAs HEMT devices. Necessary simulated band diagrams have been presented to justify our claim and we have also proposed a non-linear expression for Fermi level (EF) variation with the two-dimensional electron gas density (2DEG). We have showed that our proposed expression provides better agreement with the numerical solution than the previous approximations. Besides, expression of surface charge density (ns) variation with gate voltage (VG) obtained using our proposed model, shows better fit with the numerical simulation data in wide range of bias conditions.

Composition-Graded AlInP/AlGaAsSb/InP Type-II DHBTs With $f_{T}/f_{\rm MAX} = \hbox{450/510}\ \hbox{GHz}$

A type-II AlInP/AlGaAsSb/InP double heterojunction bipolar transistor (DHBT) with composition-graded Al content in the base is designed and grown by molecular beam epitaxy. Compared with composition-graded GaAsSb and InGaAsSb bases in DHBT, the graded AlGaAsSb base can generate a larger built-in electric field, thus reducing base transit time and improving device speed. We have fabricated AlGaAsSb graded base DHBTs and demonstrated f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> /f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> = 450/510 GHz for a 0.3 × 2 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> device.

InP DHBTs Having Lateral and Sidewall Collector Schottky Contacts

Indium-phosphide-based double heterojunction bipolar transistors having lateral and sidewall collector Schottky contacts are presented. The lateral collector structure reduces the base-collector fringing capacitance and can potentially enhance the high-frequency performance of the device. The fabrication process of the devices is described in detail.

Uni-traveling-carrier double heterojunction phototransistor photodetector

An InP/InGaAsP uni-traveling-carrier double heterojunction phototransistor (UTC-DHPT) photodetector is simulated and analyzed in a two-dimensional (2D) model utilizing a numerical device simulator (Atlas). The effects of device structure parameters on operational performance, such as responsivity and characteristic frequency, are studied in detail. Simulation results indicate that the UTC-DHPT can ease the contradiction between detection efficiency and working speed, which exists in traditional heterojun-ction phototransistor and achieve both high responsivity (≥17.93 A/W) and high characteristic frequency (≥121.68 GHz) simultaneously.

Analysis of the GaAs/GaAsBi Material System for Heterojunction Bipolar Transistors

This paper reports on the simulation of a double heterojunction bipolar transistor using the novel GaAs/GaAsBi material system. Published material parameters were used to simulate the device performance using an analytic drift-diffusion device model. DC and RF parameters were calculated as a function of emitter current density, base thickness and doping, and emitter stripe width and doping. Current gain is predicted to be between 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> at a current density of >; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a bismuth concentration of 1.5%-3%. RF performance was calculated to range from 10 to 30 GHz for fT and from 100 to 120 GHz for f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> at a current density of 105 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , base thickness of 100-200 nm, and emitter stripe width of 0.1-1 μm.

A Large-Swing 112-Gb/s Selector-Driver Based on a Differential Distributed Amplifier in InP DHBT Technology

We report a 2:1 selector-driver based on a differential distributed amplifier realized in a 0.7-μ m indium phosphide double heterojunction bipolar transistor technology. From transistors reaching fT/fmax of 320/380 GHz and a breakdown voltage (BVCEO) of 4.5 V, the selector-driver provides a differential eye amplitude of up to 6.2 and 5.9 VPP at up to 100 and 112 Gb/s, respectively, for a power consumption of 3.8 W, achieving a record swing-speed product of 620 and 660 VGb/s, respectively.

Current Gain and Offset Voltage in an InGaP/GaAsSb/GaAs Double Heterojunction Bipolar Transistor

An In0.5Ga0.5P/GaAs0.93Sb0.07/GaAs heterostructure is grown by metal-organic chemical vapor deposition and demonstrated to be an alternative to InGaP/GaAs systems for use in single heterojunction bipolar transistors (SHBTs). The In0.5Ga0.5P/GaAs0.93Sb0.07/GaAs double heterojunction bipolar transistor (DHBT) device structures are identical to the control SHBTs except for the incorporation of antimony to the base layer. The InGaP/GaAsSb/GaAs DHBT has a lower turn-on voltage than the control InGaP/GaAs SHBT. Details of the effect of the base current on the offset voltage in the studied devices are explored. The dc current gain β of the InGaP/GaAsSb/GaAs DHBT is virtually independent of collector current at 300 K. The current gain of the GaAsSb-based DHBT is greater than 40 at a very small collector current of 1 μA at 300 K. The dependence of the current gain on temperature at various collector currents is discussed. The variation of β with temperature is slight at high currents over the range of 300 K-390 K. Furthermore, the current gain of the InGaP/GaAsSb/GaAs DHBT exhibits almost no dependence on the collector-base voltage VCB, demonstrating the nonblocking “type-II” band lineup at the base/collector heterojunction.

Stability investigation for InP DHBT mm-wave power amplifier

In this article, we discuss stability issues for mm-wave monolithic integrated power amplifiers using InP double heterojunction bipolar transistor (DHBT) technology targeting E-band applications at 71–76 GHz and 81–86 GHz. Different stability detection methods based on the classical two-port K-Δs pair, linear three-port graphical analysis, system identifications, circuit modal analysis, and normalized determinant function are all reviewed. The corresponding techniques are employed to predict the occurrence of instability at 15 GHz observed during measurements on a fabricated monolithic microwave integrated circuit power amplifier. Experimental results from a redesigned power amplifier with improved stability are presented to confirm that the previously detected oscillation loop is removed using odd-mode stabilization resistors with the correct choice of values and locations. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 23: 662–674, 2013.

5.8 dBm P1 dB, high gain W-band low-noise amplifier using high breakdown voltage InP/InGaAs DHBT technology

A five-stage W-band low-noise amplifier (LNA) based on the authors' InP/InGaAs double heterojunction bipolar transistors (DHBTs) process is reported. The LNA achieves a peak gain of 33.1 dB and 7.8 dB noise figure at 81GHz. Its output-related 1 dB compression point (P1dB) lies at 5.8 dBm. The high gain and linearity of the LNA is mainly attributed to the performance of the DHBTs exhibiting a high breakdown voltage (BVceo>8.7V), a current gain cutoff frequency (fT) of 167GHz, and a maximum oscillation frequency (fmax) of 265GHz.

Future Device Modeling Trends

Good transistor models are essential for efficient computer-aided-design (CAD) of nonlinear microwave and RF circuits, monolithic microwave integrated circuits (MMICs), power amplifiers (PAs), and nonlinear RF systems. Increasingly complicated demands of the various semiconductor technologies (e.g., GaAs pHEMTs, InP double heterojunction bipolar transistors (DHBTs), silicon on insulator (SOI), LDMOS, GaN HFETs, etc.), and their applications in terms of power and frequency of operation and complexity of applied signals (e.g., modern communication signals with high peak-toaverage ratios) have placed commensurate requirements on the accuracy and generality of the device models used for design. New semiconductor material systems (e.g., GaN) have been developing at such a fast rate that conventional compact modeling approaches may not be able to keep up. These and other challenges have spawned much research into the advanced nonlinear device modeling techniques that are the focus of this article.