Heterojunction bipolar transistors with SiGe base grown bymolecular beam epitaxy

High-quality SiGe heterojunction bipolar transistors (HBTs) have been fabricated using material grown by molecular beam epitaxy (MBE). The height of parasitic barriers in the conduction band varied over the wafer, and the influence of these barriers on controller current, early voltage, and cutoff frequency were studied by experiments and simulations. Temperature-dependent measurements were performed to study the influence of the barriers on the effective bandgap narrowing in the base and to obtain an expression for the collector-current enhancement. From temperature-dependent measurements, the authors demonstrate that the collector-current enhancement of the HBTs can be described by a single exponential function with a temperature-independent prefactor     

AlGaAs/Ge/GaAs heterojunction bipolar transistors grown bymolecular beam epitaxy

An N-Al_0.22Ga_0.78As emitter, p-Ge base, and n-GaAs collector (AlGaAs/Ge/GaAs) heterojunction bipolar transistor (HBT) in the emitter-up configuration grown by molecular beam epitaxy is discussed. Devices exhibited common-emitter current gains of as high as 300 at a collector current density of 2000 A/cm² and a collector voltage of 4 V. As the device area is reduced from 50×50 to 10×40 μm, the current gain did not show significant changes, suggesting a low surface recombination velocity in the Ge base     

InP/InGaAs heterojunction bipolar transistors grown by gas-sourcemolecular beam epitaxy with carbon-doped base

The first N-p-n InP/InGaAs heterojunction bipolar transistors (HBTs) with p-type carbon doping in InGaAs are reported. P-type carbon doping in the InGaAs base has been achieved by gas-source molecular beam epitaxy (GSMBE) using carbon tetrachloride (CCl₄) as the dopant source. The resulting hole concentration in the base was 1×10¹⁹ cm^-3. HBTs fabricated using material from this growth method display good I-V characteristics with DC current gain above 500. This verifies the ability to use carbon doping to make a heavily p-type InGaAs base of an N-p-n HBT     

High-performance InP/InGaAs heterojunction bipolar transistors with highly carbon-doped base grown by chemical beam epitaxy

InP/In/sub 0.53/Ga/sub 0.47/As heterojunction bipolar transistors (HBTs) using a highly carbon-doped base are reported. High carbon doping has been achieved by chemical beam epitaxy (CBE). The resulting hole concentration in the carbon-doped base is as high as 7*10/sup 19//cm/sup 3/. To the authors' knowledge, this is the highest doping level reported using carbon. HBTs with a 20 AA spacer layer exhibited nearly ideal I-V characteristics with collector and base current ideality factor of 1.018 and 1.037, respectively. Current gain and breakdown voltage BV/sub CEO/ were 7 and 6 V, respectively.<>     

AlGaAs/InGaAs/GaAs strained-layer heterojunction bipolar transistors by molecular beam epitaxy

The growth and characteristics of the first AlGaAs/InGaAs/GaAs HBTs are reported. Layers with up to 10% indium content appeared to be free of misfit dislocations, and resulted in HBTs with good I/V characteristics which scaled with In content according to theory.     

Heavily doped base GaInP/GaAs heterojunction bipolar transistor grown by chemical beam epitaxy

The first demonstration of a GaInP/GaAs heterojunction bipolar transistor grown by chemical beam epitaxy is reported. A common-emitter current gain of 30 at a current density of 110 A/cm/sup 2/ is obtained for a beryllium base doping as high as 8*10/sup 19/ cm/sup -3/. The base sheet resistance of 140 Omega / Square Operator is among the lowest reported values.<>     

Growth characteristics of hydride-free chemical beam epitaxy and application to GaInP/GaAs heterojunction bipolar transistors

We report on the complete characterization of a hydride- and hydrogen-free chemical beam epitaxy (CBE) process for the realization of GaAs/GaInP heterojunction bipolar transistors. Alternative group V sources tertiarybutylarsine, tertiarybutylphosphine, and trisdimethylaminoarsenic are used instead of traditionally employed AsH₃ and PH₃. A very high degree of reproducibility of growth parameters (fluxes, substrate temperature, doping levels) is demonstrated. Total defect densities lower than 10 def/cm² are routinely obtained. Large-area GaInP/GaAs heterojunction bipolar transistors (HBTs) show a high current gain of 225 for base sheet resistance of 400 ohm/sq. The devices also exhibit excellent high-frequency characteristics. A cut-off frequency of 48 GHz and a maximum oscillation frequency of 60 GHz have been obtained. These results demonstrate the high potential capability of CBE for high-throughput GaInP/GaAs HBT production.     

Atomic layer epitaxy grown heterojunction bipolar transistor havinga carbon-doped base

The fabrication of a GaAs/AlGaAs heterojunction bipolar transistor (HBT) having a carbon-doped base is reported. The low diffusion coefficient of carbon makes it attractive for HBT applications since it will prevent out diffusion. The base was grown by atomic layer epitaxy (ALE), from a TMG (trimethylgallium) source that allowed the incorporation of carbon into the layer from the partially related TMG metal carbide. HBTs with common-emitter current gains of 100 were obtained at current densities of 1300 A-cm^-2     

High-speed GaAs heterojunction bipolar phototransistor grown by molecular beam epitaxy

A novel heterojunction phototransistor (HPT) structure is proposed using two base regions such that the emitter-base depletion region is located in the wide-gap material. Very small area HPTs have been fabricated on semi-insulating substrates. Maximum current gain is ? = 300. The response time, with rise time as short as 250 ps and FWHM = 320 ps, has been obtained using a picosecond pulse dye laser.     

Collector offset voltage of heterojunction bipolar transistorsgrown by molecular beam epitaxy

The collector-emitter offset voltages of InAlAs/InGaAs heterojunction bipolar transistors grown by molecular-beam epitaxy are discussed. Both the difference between emitter and collector areas and electrical asymmetry between emitter and collector junctions in these mesa-isolated transistors account for the offset voltages observed. Devices exhibited offset voltages in the range of 50-300 mV, depending on the structures and device sizes. Several electrical and geometrical factors affecting the offset voltage are discussed in detail     

Molecular beam epitaxial double heterojunction bipolar transistors with high current gains

Double heterojunction Al0.35Ga0.65As/GaAs bipolar junction transistors (DHBJTs) grown by molecular beam epitaxy (MBE) were fabricated and tested. Devices with 2000 ? and 500 ? base widths exhibited common emitter current gains of about 325 and 500, respectively, in a wide range of base and collector currents. The use of such high Al mole fraction and double heterojunctions placed stringent requirements on the growth parameter which had to be optimised and controlled very precisely to obtain such high current gains. These current gains compare with the previous best value of 120 obtained in a molecular beam epitaxial single heterojunction bipolar transistor having a 500 ?-thick base region.     

Intermodulation in heterojunction bipolar transistors

The modeling of small-signal intermodulation distortion (IMD) in heterojunction bipolar transistors (HBTs) is examined. The authors show that IMD current generated in the exponential junction is partially canceled by IMD current generated in the junction capacitance, and that this phenomenon is largely responsible for the unusually good IMD performance of these devices. Thus, a nonlinear model of the HBT must characterize both nonlinearities accurately. Finally, the authors propose a nonlinear HBT model suitable for IDM calculations, show how to measure its parameters, and verify its accuracy experimentally     

GaAsSb for heterojunction bipolar transistors

The advantages of using GaAsSb in heterojunction bipolar transistors (HBT) are discussed with emphasis on two recent experimental results in the AlGaAs/GaAsSb material system. The performances of a prototype n-p-n AlGaAs/GaAsSb/GaAs double HBT (DHBT) that exhibits stable current gain with maximum collector current density of 5×10 ⁴ A/cm², and a p-n-p AlGaAs/GaAs HBT with a superlattice GaAsSb emitter ohmic contact which has a specific contact resistivity of 5±1×10^-7 Ω-cm² across the sample, are examined     

Scaling `ballistic' heterojunction bipolar transistors

Reducing length scales in npn heterojunction bipolar transistors leads to unexpected changes in the fundamental limits of device performance. Very high p-type carrier concentrations in the base result in a reduced inelastic electron scattering rate. In addition, there exists a maximum base/collector bias above which ballistic collector transport is not possible, and correct scaling requires the n-type collector contact to be unusually heavily doped     

Submicron transferred-substrate heterojunction bipolar transistors

We report submicron transferred-substrate AlInAs/GaInAs heterojunction bipolar transistors (HBT's). Devices with 0.4-μm emitter and 0.4-μm collector widths have 17.5 dB unilateral gain at 110 GHz. Extrapolating at -20 dB/decade, the power gain cutoff frequency f_max is 820 GHz. The high f_max, results from the scaling of HBT's junction widths, from elimination of collector series resistance through the use of a Schottky collector contact, and from partial screening of the collector-base capacitance by the collector space charge     

Room temperature unpassivated InAs p-i-n photodetectors grown bymolecular beam epitaxy

An unpassivated InAs p-i-n photodetector with excellent performance at room temperature was demonstrated. The zero-bias resistance area products of the diode with 720-nm thick i-layer are 8.1 Ω-cm² at room temperature and as high as 1.3 M Ω-cm² at 77 K. At 77 K, the diode exhibits a breakdown voltage exceeding 13 V. When tested under a 500 K blackbody source, the measured detectivity limited by Johnson noise is 1.2×10¹⁰ cm-Hz^½/W at room temperature and 8.1×10 ¹¹ cm-Hz^½/W at 77 K. To our knowledge, this is the best data for a room temperature infrared detector     

InGaAs/lnP heterojunction bipolar transistor grown by all-solidsource molecular beam epitaxy

State-of-the-art InGaAs/InP heterojunction bipolar transistors were grown by all-solid source molecular beam epitaxy. Fabricated transistors showed cutoff frequencies of >100 GHz with an emitter area of 1.5×5 μm². Together with recent studies. These results demonstrate that the valved cracker technique is a very competitive nontoxic growth method     

Self-aligned AlInAs-GaInAs heterojunction bipolar transistors andcircuits

AlInAs-GaInAs heterojunction bipolar transistors (HBTs) and static flip-flop frequency dividers have been fabricated. An f_t and an f_max of 49 and 62 GHz, respectively, have been achieved in a device with a 2×5-μm² emitter. Current-mode logic (CML) was used to implement static divide-by-two and divide-by-four circuits. The divide-by-two circuit operated at 15 GHz with 82-mW power dissipation for the single flip-flop. The divide-by-four circuit operated at 14.5 GHz with a total chip power dissipation of 444 mW     

Graded-SiGe-base, poly-emitter heterojunction bipolar transistors

Si/Si_1-xGe_x heterojunction bipolar transistors (HBTs) fabricated using a low-temperature epitaxial technique to form the SiGe graded-bandgap base layer are discussed. These devices were fabricated on patterned substrates and subjected to annealing cycles used in advanced bipolar processing. These devices, which have base widths under 75 mm, were found to have excellent junction qualities. Due to the small bandgap of SiGe, the collector current at low bias is ten times higher than that for Si-base devices that have a pinched base resistance. This collector current ratio increases to more than 40 at LN₂ temperature resulting in current gains of 1600 for the SiGe-base transistors despite base sheet resistances as low as 7.5 kΩ/□     

GaAs/AlGaAs heterojunction Pnp bipolar transistors grownon (100) Si by molecular beam epitaxy

GaAs/AlGaAs Pnp heterojunction bipolar transistors (HBTs) were fabricated and tested on (100) Si substrates for the first time. A common-emitter current gain of β=8 was measured for the typical devices with an emitter area of 50×50 μm² at a collector current density of 1×10⁴ A/cm² with no output negative differential resistance up to 280 mA, highest current used. A very high base-collector breakdown voltage of 10 V was obtained. Comparing the similar structures grown on GaAs substrates, the measured characteristics clearly demonstrate that device grade hole injection can be obtained in GaAs on Si epitaxial layers despite the presence of dislocations