Collector Region Research Articles

Characteristics Improvement for an n–p–n Heterostructure Optoelectronic Switch by Introducing a Wide-Gap Layer in the Collector

In order to achieve high optical sensitivity and low holding power, a wide-gap carrier confinement layer was introduced into the collector region of an n-p-n-heterostructure optoelectronic switch. A similar device without the confinement layer was also fabricated to demonstrate the performance improvement. Both devices were found to have bistable electrical states: a high-impedance OFF state connected to a low-impedance ON state by a region of negative differential resistance. The functional characteristics were based on avalanche multiplication.

Separation of energy fractions of an electron beam by a localized nonuniformity of magnetic field in the collector region of gyrodevices

To separate the energy fractions of an electron beam, we propose that a ferromagnetic ring coaxial to the solenoid is inserted in the collector region, which can increase the efficiency of energy recovery in the case of electron deposition onto the multistage collector.

Collector-pedestal InGaAs/InP DHBTs fabricated in a single-growth, triple-implant process

This letter reports InP/In/sub 0.53/Ga/sub 0.47/As/InP double heterojunction bipolar transistors (DHBTs) employing an N/sup +/ subcollector and N/sup +/ collector pedestal-formed by blanket Fe and patterned Si ion implants, intended to reduce the extrinsic collector-base capacitance C/sub cb/ associated with the device footprint. The Fe implant is used to compensate Si within the upper 130 nm of the N/sup +/ subcollector that lies underneath the base ohmic contact, as well as compensate the /spl sim/1-7/spl times/10/sup -7/ C/cm/sup 2/ surface charge at the interface between the indium phosphide (InP) substrate and the N/sup $/collector drift layer. By implanting the subcollector, C/sub cb/ associated with the base interconnect pad is eliminated, and when combined with the Fe implant and selective Si pedestal implant, further reduces C/sub cb/ by creating a thick extrinsic collector region underneath the base contact. Unlike previous InP heterojunction bipolar transistor collector pedestal processes, multiple epitaxial growths are not required. The InP DHBTs here have simultaneous 352-GHz f/sub /spl tau// and 403-GHz f/sub max/. The dc current gain /spl beta//spl ap/38, BV/sub ceo/=6.0 V, BV/sub cbo/=5.4 V, and I/sub cbo/<50 pA at V/sub cb/=0.3 V.

Effect of a periodic action on average flow in an inhomogeneous liquid-saturated porous medium

The problem of the average flow of a viscous incompressible fluid saturating a stationary porous incompressible matrix under a periodic action is considered. It is shown that a spatial inhomogeneity of the medium porosity leads to an average fluid flow, quadratically dependent on the action amplitude, in the direction of increase in porosity. In particular, this means that wave action on an oil reservoir could lead to fluid flow on the interfaces from low-porosity,weakly permeable collector regions into high-porosity regions, for example, to flow from blocks to fractures in fractured porous reservoirs, which makes it possible to enhance oil production.

Device Simulation and Design Optimization for Diamond Based Insulated-gate Bipolar Transistors

ABSTRACTA diamond based insulated gate bipolar transistor is incorporated into a two-dimensional device simulator (MEDICI) to examine the current gain (β) and potential distribution across the device. Initially, work has focused on an important component of IGBT structure, the PNP bipolar transistor, which has been simulated and is reported upon in this paper. Empirical parameters for emitter and collector regions were used. Various carrier concentrations for base region were used to optimize the simulation. It was found that decreasing the thickness of base region leads to an increase in current gain. A buffer layer is needed to prevent the punch-through at low carrier concentration in the base region. Various approaches of increasing the current gain are also discussed in this paper.

Proton radiation effects in vertical SiGe HBTs fabricated on CMOS-compatible SOI

Proton radiation effects in vertical SiGe HBTs fabricated on CMOS-compatible silicon-on-insulator (SOI) are investigated for the first time. Proton irradiation at 63 MeV is found to introduce base leakage current at low base-emitter voltage, delay the onset of Kirk effect at high injection, and increase the frequency response of SiGe HBTs on SOI. The latter two effects are in contrast to those found in conventional bulk SiGe HBTs. Proton irradiation also generates positive fixed oxide and interface charge in the buried oxide, which alters both M-1 and BV/sub CEO/ in the SiGe HBT by modulating the electric field in the collector region.

Analysis of Transit Times and Minority Carrier Mobility in n-p-n 4H-SiC Bipolar Junction Transistors

An analysis of the transit times and minority carrier mobility in n-p-n 4H-SiC RF bipolar junction transistors is presented. These parameters were extracted from small signal RF measurements on 4H-SiC RF transistors with three different base thicknesses: 100, 140, and 200 nm. The study shows that the room temperature minority carrier electron mobility is 215 cm/sup 2//V/spl middot/s for a base Al doping of N/sub B/=4/spl times/10/sup 18/ cm/sup -3/. The analysis reveals that the collector charging time /spl tau//sub C/ and the parasitic charging time /spl tau//sub P/ from the capacitance between metal pads and the underlying collector region have a significant effect on the transistors RF performance. The calculated RF gain is in good agreement with the measured results.

Different Failure signatures of multiple TLP and HBM Stresses in an ESD robust protection structure

The failure signatures of a grounded-base NPN bipolar ESD protection under multiple TLP and HBM stresses are analyzed. For this particular device having a graded collector region, multiple TLP or HBM stresses result in different types of defects. OBIC techniques and TCAD simulations are used to thoroughly analyze the involved physical mechanisms.

Photoreflectance characterization of InP∕GaAsSb double-heterojunction bipolar transistor epitaxial wafers

We report photoreflectance (PR) measurements of InP∕GaAsSb double-heterojunction bipolar transistor epitaxial wafers grown by metalorganic vapor-phase epitaxy and discuss the correlation between the spectra and the electrical characteristics of the emitter–base (E∕B) heterojunctions. The origin of Franz–Keldysh oscillations (FKOs) in the PR spectra was identified by step etching of the samples. The current–voltage characteristics of the E∕B heterojunctions were examined by fabricating devices. FKOs from both the emitter and collector regions were observed in the wafers where the recombination forward current at the E∕B heterojunction was suppressed. In contrast, when the recombination current was significant, no emitter-related FKOs were observed. The absence of the FKOs from the emitter indicates the high concentration of recombination centers at the E∕B heterojunction.

Non‐destructive, room temperature characterization of wafer‐sized III–V semiconductor device structures using contactless electromodulation and wavelength‐modulated surface photovoltage spectroscopy

AbstractWe review the use of the contactless methods of photoreflectance (PR), contactless electroreflectance (CER) and wavelength modulated differential surface photovoltage spectroscopy (DSPS) for the nondestructive, room temperature characterization of a wide variety of wafer‐scale III–V semiconductor device structures. Some systems that will be discussed include heterojunction bipolar transistors (including the determination of the built‐in fields/doping levels in the emitter and collector regions, alloy composition, and dc current gain factor), pseudomorphic GaAlAs/InGaAs/GaAs high electron mobility transistors (including the determination of the composition, width, and two‐dimensional electron gas density in the channel), InGaAsP/InP quantum well edge emitting lasers (including the detection of p‐dopant interdiffusion), vertical‐cavity surface‐emitting lasers (determination of fundamental conduction to heavy‐hole excitonic transition and cavity mode). (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Comprehension and modelling of heterojunction phototransistors operated in the Gummel-plot and common-emitter modes

Fabrication, characterization and modelling of heterojunction phototransistors (HPTs) are reported. The common-emitter (with current-biased base) and Gummel-plot (with voltage-biased base) modes are employed to characterize and fully comprehend what differences exist between the current- and voltage-biased HPT's performance. The results of further studies include the case when a series of different optical-power injection levels is illuminated at our HPTs. The performance of the current- and voltage-biased HPTs was also compared to that from a newly proposed HPT model and related equivalent circuit with good agreement found. Although an independent voltage source can be used to tune the operating point of a heterojunction bipolar transistor to a higher current level where the dc current gain is larger, the photocurrent generated within the base–collector (B–C) region offers few contributions to the final collector photocurrent. The optical gain obtained from the HPT biased using a high voltage is even smaller than that of the HPT with a floating base. It is concluded that (i) a current-biased HPT's dc base current and photocurrent generated within the B–C region entirely flow into the base–emitter (B–E) junction so that the device's optical gain is enhanced; (ii) however, no enhancement of optical gain for a HPT will be obtained using dc base bias, since the dc current gain is independent of collector (or base) current; (iii) a voltage-biased HPT behaves like a p–i–n photodiode and (iv) electrical base bias using a high external voltage source with a large series resistance is a possible way to enhance the optical gain of a HPT.

Base resistance scaling for SiGeC HBTs with a fully nickel-silicided extrinsic base

A novel SiGeC HBT process with a quasi-self-aligned emitter-base architecture and a fully nickel-silicided extrinsic base region has been developed. A very low total base resistance R/sub B/ was achieved along with simultaneous NiSi formation on the polycrystalline emitter and collector regions. Uniform silicide formation was obtained across the wafer, and the resistivity of the Ni(SiGe:C) silicide layer was 24 μ/spl Omega//spl middot/cm. About 50-100 nm of lateral growth of silicide underneath the emitter pedestal was observed. DC and HF results with balanced 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> values of 41/42 GHz were demonstrated for 0.5×10μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> transistors.

Forward Active and Blocking Performance of 4H-SiC Bipolar Junction Transistors

ABSTRACTWe evaluate the performance capabilities and limitations of high voltage 4H-SiC based Bipolar Junction Transistors (BJTs). Experimental forward characteristics of a 4kV BJT are studied and simulations are employed to determine the factors behind the higher than expected specific on-resistance (Ron,sp) for the device. The impact of material (minority carrier lifetimes), processing (surface recombination velocity) and design (p contact spacing from the emitter mesa) parameters on the forward active performance of this device are discussed and ways to lower Ron,sp, below the unipolar level, and increase the gain (β) are examined. A correlation between the open base blocking behavior (forward blocking) and the current gain (forward active) for 4H-SiC based high-voltage BJTs with lightly doped collector regions is presented and experimental device characteristics are utilized to verify our numerical analysis.

Low-Frequency Parasitic Space-Charge Oscillations in the Helical Electron Beam of a Gyrotron

We developed a medium-power pulsed gyrotron equipped with diagnostic systems for studying low-frequency parasitic space-charge oscillations in the helical electron beam and the energy spectrum of electrons in the collector region. Methods for suppressing parasitic oscillations are proposed and tested. An explanation of the mechanism of suppression of these oscillations is given.

Equivalent circuit model for the electrical analysis of a spin bipolar transistor

An equivalent circuit model for the switching performance of a spin bipolar transistor composed of a nonmagnetic metal film (N) sandwiched between two ferromagnetic metal films (F1 and F2) is suggested. The ‘ON’ or ‘OFF’ operation of this equivalent circuit model is simulated depending on the orientation of the magnetization of F1 and F2 rather than on the strength of the external magnetic field. Changing the coupling coefficient, by tuning the ratio of two inductances (L1:L2) like a transformer and a parallel vari-able resistance R4 connected to L2 at the collector region, one can explain the magnetic resistance ratio based on the orientation of spin-polarized electrons. The simulation results show that the electrical per-formance is consistent with the physical operation of the spin bipolar transistor. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Temperature dependence of the electron impact ionization in InGaP-GaAs-InGaP DHBTs

Temperature dependence of electron impact ionization in InGaP-GaAs-InGaP double heterojunction bipolar transistors (DHBTs) were comprehensively studied in the temperature range of 300 to 450 K. It has been found that, as the temperature increases, the electron multiplication in the InGaP collector is found to be weakly reduced, which results in a relatively small negative temperature dependence of junction breakdown. The temperature dependence of electron impact ionization at elevated temperatures for InGaP material is investigated based on the electron multiplications measured from the InGaP collector region. An empirical expression is obtained to predict the electron ionization coefficients at elevated temperature up to 450 K in the electric field range of 380 to 650 kV/cm. As compared to InP and GaP binaries, the ternary InGaP shows a lower electron ionization coefficient and much weaker temperature dependence. We found that, introducing additional scattering mechanism such as alloy scattering would provide a better interpretation on the low electron impact ionization and its weak temperature dependence observed in InGaP.

Study of improved reverse recovery in power transistor incorporating universal contact

The improvement in reverse recovery of power NPN bipolar transistor (BJT) through incorporation of “universal contact” in the base is studied in detail. It is shown that use of universal contact allows redistribution of base current in saturation from collector region where recombination lifetime is high to extrinsic base region where effective recombination lifetime is low. The reverse recovery time decreases as collector current density increases but increases as collector breakdown voltage increases. The improvement in reverse recovery is accompanied with an increase in collector–emitter voltage in the ON state. For low voltage transistors and high voltage transistors at low collector current densities, the increase is primarily due to reduction in reverse current gain. For high breakdown voltage transistors, the use of universal contact results in early onset of quasi-saturation effect and results in degradation in ON state voltage at high collector current densities.

Theory of a room-temperature silicon quantum dot device as a sensitive electrometer

We consider theoretically the use of a room-temperature silicon quantum dot based device for electrometer applications. The low power device includes two split gates that quantize the electronic energy levels in the emitter and collector regions. The base consists of a silicon quantum dot buried in silicon dioxide. The small size of the dot and quantization of the states in the leads combined to allow the device to operate at room temperature. The nonlinear current–voltage characteristics can be significantly altered by small changes to the potential of the split gates. Power dissipation in the device therefore changes with the split gate voltage, and this can be exploited in electrometer applications. A simple model of the power dissipated when the device is part of a microwave resonant inductor-resistor-capacitor tank circuit suggests that large changes in device power can be achieved by changing the gate voltage, thereby forming a measurable signal. We also demonstrate that the power dissipation in the device changes as the base width is varied, and that the current through the device increases exponentially with a decrease in base width.

High-reliability InGaP/GaAs HBTs with 153 GHz f T and 170 GHz f max

High-reliability high-performance InGaP/GaAs hetero-junction bipolar transistors (HBTs) are described. A novel layer structure, ion implantation into the external collector region, and an emitter-surrounding ledge overlaid by base metal enhance both performance and reliability. High values of fT and fmax both greater than 150 GHz are attained with a long MTTF of 1011 h at a junction temperature of 125°C under severe bias conditions.

Spin-polarizing properties of the InAs/(AlSb)/GaMnSb/(AlSb)/InAs ferromagnetic resonant interband tunneling diode

We theoretically investigate the low-temperature spin-dependent current-voltage characteristics of the ferromagnetic resonant interband tunneling diode (FRITD). The simulations are based on a transmission formulation of the effective bond-orbital method (EBOM), which self-consistently includes both the electrostatic potential and the magnetic exchange interaction. Despite negligible spin splitting in the InAs emitter and collector regions, this type-II InAs/(AlSb)/GaMnSb/(AlSb)/InAs structure can function either as a source of spin-polarized electrons, whose polarity depends on the applied bias, or as a spin valve. For unpolarized emitter electrons, the spin polarization of carriers transmitted to the collector can be as high as \ensuremath{\approx}90%. We consider both thicker-well structures, in which the interband tunneling occurs primarily via light-hole-like states, and thinner-well devices whose transport is dominated by heavy-hole transitions. Since the maximum FRITD operating temperature is limited primarily by the Curie temperature in the GaMnSb hole quantum well, the same favorable device performance may be achievable at 77 K by employing the digital incorporation of Mn into the center of a GaSb hole well.