Early voltage in double heterojunction bipolar transistors

The Early voltage for abrupt double heterojunction bipolar transistors (DHBTs) has been calculated by using an effective junction velocity (S_c) at the base-collector heterojunction. S_c is obtained by self-consistently partitioning thermionic and quantum mechanical tunneling currents. Unlike single heterojunction bipolar transistors (SHBTs), the Early voltage varies very rapidly at low reverse bias and approaches the SHBT-limit at sufficiently high reverse bias. This is attributed to the presence of an energy barrier at the b-c heterojunction     

Neutral base recombination and its influence on the temperaturedependence of Early voltage and current gain-Early voltage product inUHV/CVD SiGe heterojunction bipolar transistors

We present the first comprehensive investigation of neutral base recombination (NBR) in ultra-high vacuum/chemical vapor deposited (UHV/CVD) SiGe heterojunction bipolar transistors (HBT's), and its influence on the temperature characteristics of Early voltage (V_A ) and current gain-Early voltage product (βV_A). We show that a direct consequence of NBR in SiGe HBT's is the degradation of V_A when transistors are operated with constant-current input (forced-I_B) as opposed to a constant-voltage input (forced-V_BE). In addition, experimental and theoretical evidence indicates that with cooling, V_A in SiGe HBT's degrades faster than in Si bipolar junction transistors (BJT's) for forced-I_B mode of operation. Under the forced-V_BE mode of operation, however, SiGe HBT's exhibit a thermally-activated behavior for both V_A and βV_A, in agreement with the first-order theory. The differences in V_A as a function of the input bias and temperature for SiGe HBT's are accurately modeled using a modified version of SPICE. The performance of various practical SiGe HBT circuits as a function of temperature, in the presence of NBR, is analyzed using this calibrated SPICE model     

Dynamic Early effect in heterojunction bipolar transistors

A theory of base transport in an abrupt-junction heterostructure bipolar transistor (HBT) is developed in the diffusion limit. The theory is valid for a continuous range of emitter injection energies Δ and accounts for the Early effect in both the static and the high-frequency limits. Small-signal network parameters strongly depend on Δ and differ from those in a graded emitter-base junction HBT     

Early voltage in very-narrow-base bipolar transistors

It is shown that for VLSI devices with very narrow base widths (less than 0.1 μm), the velocity saturation effect gives a substantial increase in Early voltage and a corresponding beneficial increase in output resistance. The theory is discussed, and practical results are presented     

Ideality factor of extrinsic base surface recombination current in AlGaAs/GaAs heterojunction bipolar transistors

Various structures of npn AlGaAs/GaAs heterojunction bipolar transistor have been fabricated to examine the ideality factor for extrinsic base surface recombination. Comparison of the measured results indicates that the base surface recombination current increases exponentially with the base-emitter voltage with an ideality factor of 1, rather than 2. This finding agrees with a published theoretical analysis (see Tiwari et al., J. Appl. Phys., vol.64, p.5009, 1988).<>     

Silicon-germanium base heterojunction bipolar transistors bymolecular beam epitaxy

The devices were fabricated using molecular-beam epitaxy (MBE), low-temperature processing, and germanium concentrations of 0, 6%, and 12%. The transistors demonstrate current gain, and show the expected increase in collector current as a result of reduced bandgap due to Ge incorporation in the base. For a 1000-Å base device containing 12% Ge, a six-times increase in collector current was measured at room temperature, while a 1000-times increase was observed to 90 K. The temperature dependence of the collector current of the Si_0.88Ge_0.12 base transistor is consistent with a bandgap shrinkage in the base of 50 meV. For the homojunction transistors, base widths as thin as 800 Å were grown, corresponding to a neutral base width of no more than 400 Å     

Experimental comparison of base recombination currents in abrupt and graded AlGaAs/GaAs heterojunction bipolar transistors

The relative importance of the base bulk recombination current and the base-emitter junction space charge recombination current is examined for AlGaAs/GaAs HBTs with different grading schemes in the base-emitter junction. Experimental results demonstrate that, in abrupt HBTs, the base bulk recombination current is larger, and the base current increases with the base-emitter bias with an ideality factor of approximately 1. In contrast, in graded HBTs, the space charge recombination current dominates and the base current ideality factor is approximately 2. These experimental results agree well with a published theoretical calculation.<>     

基区复合电流对双极晶体管厄利电压的影响

推导了在考虑了基区复合电流后双极晶体管厄利电压的理论表达式。用该表达式计算了 Si/Si Ge异质结双极晶体管的厄利电压 ,并且与仿真结果进行了比较。比较结果表明 ,两种情况下计算出的厄利电压值符合良好     

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     

Early voltage uniqueness test for bipolar junction transistors

A technique is described for the direct visual comparison of the common emitter output characteristic?at a chosen collector current, in the forward active mode?of a junction transistor subjected alternately to base-emitter voltage drive and base current drive. The Early effect is characterised by a unique parameter, the Early voltage, only if the two curves can be shown to exhibit coincidence in the nonsaturated region.     

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     

Significant operating voltage reduction on high-speed GaAs-based heterojunction bipolar transistors using a low band gap InGaAsN base layer

We report the fabrication of double heterojunction bipolar transistors (DHBTs) with the use of a new quaternary InGaAsN material system that takes advantage of a low-energy band gap E/sub G/ in the base to reduce operating voltages in GaAs-based electronic devices. InGaP/In/sub 0.03/Ga/sub 0.97/As/sub 0.99/N/sub 0.01//GaAs DHBTs with improved band gap engineering at both heterojunctions exhibit a DC peak current gain over 16 with small active emitter area. The use of the lattice-matched In/sub 0.03/Ga/sub 0.97/As/sub 0.99/N/sub 0.01/ (E/sub G/=1.20 eV) base layer allows a significant reduction of the turn-on voltage by 250 mV over standard InGaP/GaAs HBTs, while attaining good high-frequency characteristics with cutoff frequency and maximum oscillation frequency as high as 40 GHz and 72 GHz, respectively. Despite inherent transport limitations at the present time, which penalize peak frequencies, this novel technology provides comparable RF performance to conventional devices with a GaAs control base layer but at much lower operating base-emitter bias conditions. This technical progress should benefit to the next generation of RF circuits using GaAs-based HBTs with lower power consumption and better handling of supply voltages in battery-operated wireless handsets.     

锗硅异质结双极晶体管空间辐射效应研究进展

异质结带隙渐变使锗硅异质结双极晶体管(SiGe HBT)具有良好的温度特性,可承受-180~+200 ℃的极端温度,在空间极端环境领域具有诱人的应用前景。然而,SiGe HBT器件由于材料和工艺结构的新特征,其空间辐射效应表现出不同于体硅器件的复杂特征。本文详述了SiGe HBT的空间辐射效应研究现状,重点介绍了国产工艺SiGe HBT的单粒子效应、总剂量效应、低剂量率辐射损伤增强效应以及辐射协同效应的研究进展。研究表明,SiGe HBT作为双极晶体管的重要类型,普遍具有较好的抗总剂量和位移损伤效应的能力,但单粒子效应是制约其空间应用的瓶颈问题。由于工艺的不同,国产SiGe HBT还表现出显著的低剂量率辐射损伤增强效应响应和辐射协同效应。     

An improved Early voltage model for advanced bipolar transistors

An improved Early voltage model reflecting the effect of bias variation is developed. The bias dependencies of the Early voltage are more prominent as the base width of the bipolar transistor decreases. Thus, using the conventional constant Early voltage model can result in considerable errors in modeling the advanced bipolar transistors which possess very thin base region. Comparisons between the present model and the conventional model at different bias conditions support this assertion. SPICE simulations are performed to demonstrate the impact of this study on the small-signal performance of bipolar-transistor integrated circuits     

A theory of shot noise in quantum wells and applications inresonant tunneling heterojunction bipolar transistors

Some semiclassical arguments are presented to show that the noise associated with the current through a resonant tunnel (RT) diode is reduced by the feedback through the modulation of the barriers by the space charge in the well, and at high frequencies by the reduction in the velocity spread. Theoretical calculations of shot noise are carried out on a double-barrier, one-well structure. The results show that the noise power is a function of the energy bandwidth of the transmitted electrons and that the noise may be significantly reduced by the quantum wells. These results can be applied to heterojunction bipolar transistors that contain a quantum well, and it is shown that these resonant tunneling heterojunction bipolar transistors (RTHBTs) should have a lower noise figure than homojunction transistors     

The effects of base dopant diffusion on DC and RF characteristicsof InGaAs/InAlAs heterojunction bipolar transistors

The effects of base p-dopant diffusion at junction interfaces of InGaAs/InAlAs HBTs with thin base thicknesses and high base dopings are reported. It is shown that HBTs with compositionally graded emitter-based (E-B) junctions are very tolerant to base dopant outdiffusion into the E-B graded region. The RF performance is nearly unaffected by the diffusion, and the DC current gain and E-B junction breakdown voltages are improved with finite Be diffusion into the E-B graded region     

Diode ideality factor for surface recombination current inAlGaAs/GaAs heterojunction bipolar transistors

n-p-n AlGaAs/GaAs heterojunction bipolar transistors of various emitter areas have been fabricated to examine the diode ideality factor for surface recombination. These transistors are fabricated with and without exposed extrinsic base surfaces. Comparison of the measured results indicates that the base surface recombination current increases exponentially with the base-emitter voltage with an ideality factor which is closer to 1 than 2(1<n<1.33). This finding agrees with a published theoretical analysis of base surface recombination in HBTs. This study is compared with other experimental work     

Critical spacing between emitter and base in InGaP heterojunction bipolar transistors (HBTs)

In this paper, the influence of the spacing between the emitter and the base on the performance of InGaP heterojunction bipolar transistors (HBT) was experimentally studied. We found that the emitter to base spacing can be reduced to as small as 0.6 /spl mu/m without causing a significant drop in the current gain. The reduction in emitter-to-base spacing, however, leads to improvement in high-frequency performance and device phase noise. For optimal dc, RF, and low-frequency noise performances, we have determined that a critical spacing of 0.6/spl sim/0.8 /spl mu/m between the emitter and the base of an InGaP HBT is required.