Effect of exponentially graded base doping on the performance ofGaAs/AlGaAs heterojunction bipolar transistors

The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5×10¹⁹ cm^-3 at the emitter edge to 5×10¹⁸ cm^-3 at the collector edge. The built-in field due to the exponentially graded doping profile significantly reduces base transit time, despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping of 1×10¹⁹ cm^-3 , the cutoff frequency is increased from 22 to 31 GHz and maximum frequency of oscillation is increased from 40 to 58 GHz. Exponentially graded base doping also results ill consistently higher common-emitter current gain than uniform base doping, even though the Gummel number is twice as high and the base resistance is reduced by 40%     

Pyrolysis of tertiarybutylphosphine at low pressure

The pyrolysis of tertiarybutylphosphine (TBP) has been studied in the low pressure conditions used for chemical beam epitaxy (CBE). The pyrolysis studies were carried out in low pressure reactors of two different configurations, one of which is a cracker cell designed for use in a CBE system. The reaction products were studied using a quadrupole mass spectrometer. The products observed are accounted for by a reaction mechanism involving homolysis of the parent TBP molecule to produce PH₂ and C₄H₉ radicals. These undergo subsequent reactions to form the stable products C₄H₈, PH₃ and H₂, with smaller amounts of P and P₂ being produced. The production of the sub-hydride PH₂ using this cracker cell design indicates that the use of partially cracked TBP may be a promising technique for reducing the amount of carbon incorporated into the growing epitaxial layer.     

Design criteria of the near-millimeter wave quasi-optical monolithic diode-grid frequency multiplier array

The high-frequency performance along with the optimum designs and operating conditions of near-millimeter wave quasi-optical monolithic diode-grid frequency multiplier arrays have been studied and will be presented in this paper. The limitations of the development of nearmillimeter wave quasi-optical monolithic diode-grid frequency multiplier arrays will be discussed in detail. The optimum operating conditions and performance of different device structures are presented along with the associated device physics. The optimum designs, operating conditions and performance of the monolithic diode-grid frequency multiplier array will also be discussed based upon the temperature distribution study on the diode-grid.     

A comparison of commercially available quasistatic meters and methods

The capacitance-voltage (C-V) technique is one of the most powerful and direct methods to investigate interface traps in metal-insulator-semiconductor (MIS or MOS) related devices. As the C-V technique is of such fundamental importance in detecting and monitoring process related defects the systematic measurement concerns, misinterpretations and limitations associated with the equipment used to implement this technique must be fully understood and characterized. This study reports the results of a detailed comparison of both the (raw) measured C-V curve and the (analyzed) interface trap density versus energy data obtained using commercially available quasistatic meters, specifically the Hewlett-Packard (HP) model 4140B quasistatic/dc picoammeter and the Keithley model 595 quasistatic meter.     

Schottky barrier heights of n-type and p-type Al0.48In0.52As

The authors report electrical measurements on four different metal contacts which formed Schottky barriers to lightly doped complementary n- and p-type Al_0.48In_0.52As epitaxial material grown by molecular beam epitaxy on semi-insulating InP substrates. The Schottky contact metals studied were Au, Al, Pt, and tri-layer Ti/Pt/Au. The Schottky barrier heights varied from 0.560 eV for Al on n-type AlInAs to 0.905 eV for Al on p-type AlInAs, with intermediate values for the other metals studied. The sum of n- and p-type Schottky barrier heights for each metal contact ranged from 1.440 to 1.465 eV, in good agreement with the accepted Al_0.48In_0.52As bandgap value of 1.45 eV     

Enhancement of high-temperature high-frequency performance ofGaAs-based FETs by the high-temperature electronic technique

This paper reports the effects of high temperature on high-frequency/high-speed field effect transistors (FETs), particularly GaAs-based MESFETs and HEMTs. The high-temperature electronic technique (HTET) was employed to stabilize and improve the performance of these devices at high temperatures. This work focuses on detailed high-temperature experiments of high-frequency scattering parameters of various transistors. Comparable gain level to that obtained at room temperature was achieved at elevated temperature through the use of the HTET     

Molecular beam epitaxy growth of TmP/GaAs and transistor action inGaP/TmP/GaAs heterostructures

The growth of thulium phosphide (TmP) by molecular beam epitaxy (MBE) on GaAs substrate is reported. Good epilayer quality was demonstrated through X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM) analysis. The closely lattice matched TmP layer was n-type with an electron concentration of 1.6×10²¹ cm^-3 and a room temperature mobility of 4.8 cm²V^-1s^-1. The Schottky barrier height determined from 1/capacitance² (1/C²) versus voltage (V) measurements is about 0.81 eV which agrees well with the value obtained through the current-voltage (I-V) measurements. In this work, we also report transistor action in a GaP/TmP/GaAs structure, for which chemical bonding techniques were employed. From I-V measurements, a common base current gain α≈0.55 at V_CB=0 was obtained at room temperature     

Limitations of the back-to-back barrier-intrinsic-n+(BIN) diode frequency tripler

Problems of the back-to-back GaAs barrier-intrinsic-n⁺ (BIN) diode frequency tripler concept along with the associated device physics are presented. The back-to-back GaAs BIN diode structure was originally proposed to have an intrinsic cutoff frequency close to 1 THz and to be a highly efficient millimeter-wave frequency tripler. Frequency limitations will be discussed to explain the failure of the back-to-back GaAs BIN diode as a millimeter-wavelength device. Optimization is also carried out to explore the possibility of improving the high-frequency performance by modifying the BIN diode structure     

Epitaxial growth and characterization of DyP/GaAs, DyAs/GaAs, and GaAs/DyP/GaAs heterostructures

There is a significant interest in the area of improving high temperature stable contacts to III-V semiconductors. Two attractive material systems that offer promise in this area are dysprosium phosphide/gallium arsenide (DyP/GaAs) and dysprosium arsenide/gallium arsenide (DyAs/GaAs). Details of epitaxial growth of DyP/GaAs and DyAs/GaAs by molecular beam epitaxy (MBE), and their characterization by x-ray diffraction, transmission electron microscopy, atomic force microscopy, Auger electron spectroscopy, Hall measurements, and high temperature current-voltage measurements is reported. DyP is lattice matched to GaAs, with a room temperature mismatch of less than 0.01% and is stable in air with no sign of oxidation, even after months of ambient exposure. Both DyP and DyAs have been grown by solid source MBE using custom designed group V thermal cracker cells and group III high temperature effusion cells. High quality DyP and DyAs epilayer were consistently obtained for growth temperatures ranging from 500 to 600°C with growth rates between 0.5 and 0.7 μm/h. DyP epilayers are n-type with electron concentrations of 3 × 10²⁰ to 4 × 10²⁰ cm⁻³, room temperature mobilities of 250 to 300 cm²/V·s, and a barrier height of 0.81 eV to GaAs. DyAs epilayers are also n-type with carrier concentrations of 1 × 10²¹ to 2 × 10²¹ cm⁻³, and mobilities between 25 and 40 cm²/V·s.     

Millimeter wave monolithic high electron mobility (HEM) varactor diode-grid frequency tripler arrays

High Electron Mobility (HEM) varactor structures have been studied for millimeter-wave monolithic diode-grid frequency tripler array applications. The improved HEM varactor diode structures provide a highly nonlinear C-V characteristic (i.e., a steep slope of the C-V curve and a large capacitance ratio) which produces high harmonic generation efficiency and reduce the power requirement for efficiently pumping each device. The effects of the light illumination on the C-V characteristics of the Barrier-Intrinsic-N⁺ (BIN) varactor diode have also been studied and the results will be discussed in this paper. In the development of a monolithic diode-grid frequency multiplier array, the low-loss quasioptical configuration is used for the construction of the multiplier circuit. The study of the effects of the light illumination on the C-V characteristics of varactor diode is important in understanding the potential applications of the quasi-optical varactor diode-grid frequency multiplier array circuit.