J.R. Velebir

High-reliability GaAs-AlGaAs HBTs by MBE with Be base doping and InGaAs emitter contacts

The authors have developed a modified MBE growth process to produce high-gain n-p-n GaAs-AlGaAs heterojunction bipolar transistors (HBTs) with a mean time to failure (MTTF) of 1.5*10/sup 8/ h at 125 degrees C. Beryllium incorporation and diffusion are controlled through a combination of reduced substrate temperature and increased As/Ga flux ratio during MBE growth, resulting in extremely stable HBT profiles. The authors also demonstrate graded InGaAs surface layers with nonalloyed refractory metal contacts that significantly improve ohmic reliability compared to alloyed AuGe contacts. The ability to produce robust HBTs by MBE is critically important to this technology.<<ETX>>

Integrated complementary HBT microwave push-pull and Darlington amplifiers with p-n-p active loads

The authors report the microwave results of complementary heterojunction bipolar transistor (HBT) amplifiers that integrate both n-p-n and p-n-p devices on the same chip using selective molecular beam epitaxy (MBE). An HBT wideband amplifier utilizing the Darlington configuration and implementing a p-n-p active load has a gain of 7.5 dB and a bandwidth from DC to 2.5 GHz. A complementary push-pull amplifier has a saturated output power of 7.5 dBm at 2.5 GHz. >

InAlAs/InGaAs HBT X-band double-balanced upconverter

The authors report on an InAlAs/InGaAs HBT Gilbert cell double-balanced mixer which upconverts a 3 GHz IF signal to an RF frequency of 5-12 GHz. The mixer cell achieves a conversion loss of between 0.8 dB and 2.6 dB from 5 to 12 GHz. The LO-RF and IF-RF isolation are better than 30 dB at an LO drive of +5 dBm across the RF band. A predistortion circuit is used to increase the linear input power range of the LO port to above +5 dBm. Discrete amplifiers designed for the IF and RF frequency ports make up the complete upconverter architecture which achieves a conversion gain of 40 dB for an RF output bandwidth of 10 GHz. The upconverter chip set fabricated with InAlAs/InGaAs HBTs demonstrates the widest gain-bandwidth performance of a Gilbert cell based upconverter compared to previous GaAs and InP HBT or Si-bipolar ICs. >

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

The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5*10/sup 19/ cm/sup -3/ at the emitter edge to 5*10/sup 18/ cm/sup -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*10/sup 19/ cm/sup -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%.<<ETX>>

Effect of molecular‐beam epitaxy growth conditions on GaAs–AlGaAs heterojunction bipolar transistor performance: Beryllium incorporation and device reliability

We have studied the effect of molecular‐beam epitaxy (MBE) growth conditions on the performance and reliability of npn GaAs–AlGaAs heterojunction bipolar transistors (HBTs). Wafers grown under normal conditions yield devices with high current gain, but suffer premature failure due to interstitial beryllium diffusion from the base into the graded AlGaAs emitter. Wafers grown with high arsenic/gallium flux ratio and reduced substrate temperature during base deposition have high current gain, and are extremely reliable. Mean time to failure, as defined by a 10% reduction in original current gain, is ≳ 108 h at 125 °C junction temperature for devices grown using conditions optimized for device reliability. We believe the ability to produce high reliability HBTs by MBE is vital to future applications of this technology.

Complementary HBT push-pull amplifier by selective MBE

Microwave performance results are presented of the first monolithically integrated GaAs-AlGaAs complementary HBT push-pull amplifier fabricated using selective molecular beam epitaxy and a merged HBT process. The push-pull amplifier integrates four n-p-n transistors with one p-n-p transistor on the same GaAs chip. The amplifier has a sharp DC characteristic curve with no crossover offset, a voltage swing of 6.3 V using a 9-V supply, and a linear voltage gain of 20. The bandwidth is DC to 2.5 GHz, with a saturated output power of 7.4 dBm at 2.5 GHz.<<ETX>>

A novel heterojunction bipolar transistor active feedback design

This paper reports on the results of a novel active feedback amplifier design using heterojunction bipolar transistors. The design incorporates positive feedback to increase the gain bandwidth response by as much as 50 %. The active feedback amplifier achieves a gain of 13.8 dB and a 3-dB bandwidth of 15.6 GHz. The active feedback is economical in size in comparison to a spiral inductor implementation. In addition, the active feedback network includes a means for electronically tuning the active feedback circuit in order to adjust the bandwidth response. A two-stage design achieves a tuneable bandwidth from 4-10 GHz with a fixed gain of 20 dB. The tuneability that this design offers is a convenient means for recovering from gain and bandwidth degradation due to process variation and fixture parasitics.<<ETX>>

Selective molecular‐beam epitaxy for integrated npn/pnp heterojunction bipolar transistor applications

We have developed a selective molecular‐beam epitaxy (MBE) growth process for the production of complementary npn and pnp heterojunction bipolar transistors (HBTs) on the same GaAs substrate. The resulting devices have excellent dc and microwave characteristics, with no degradation observed due to the additional growth and processing steps required to monolithically integrate npn and pnp HBTs. We believe the ability to fabricate high‐quality complementary HBT devices and circuits will greatly expand the application base of MBE‐grown heterojunction bipolar transistors.

Low power consumption InAlAs-InGaAs-InP HBT SPDT PIN diode X-band switch

Results for the first monolithic single-pole, double-throw (SPDT) X-band PIN diode switch fabricated with InAlAs-InGaAs HBTs lattice matched to InP are reported. The switch achieves performance similar to that of a GaAs implementation but with half the power consumption. The insertion loss is 0.89 dB and the off-isolation is >35 dB at 10 GHz. The IP3 is 29.6 dBm and the total power consumption is 10.2 mW. Monolithic integration of PIN diodes with an InP-based HBT process provides monolithic switch functions for use in microwave and millimeter-wave communication systems.<<ETX>>

Measurement of ultra‐abrupt doping transitions using capacitance versus voltage techniques

In this work we report on methodologies and procedures to obtain the doping profile of semiconductor homo‐ and heterostructure devices with ultra‐abrupt doping transitions at or near the surface of a device or test structure using capacitance–voltage measurement techniques. Novel methods to obtain the complete carrier distribution (or ‘‘spike’’) of structures containing single of multiple planar (also known as delta) doped layers will be addressed. Techniques to measure the true doping profile of abrupt step and staircase doped structures will also be discussed. Extensive numerical models and methods have been developed to accurately extract doping and carrier concentration profiles of traditional and two‐dimensional electron (or hole) gas devices. The analysis and acquisition techniques which have been developed are applicable to all group IV and III–V compound semiconductor devices containing p‐n homojunctions or heterojunctions, Schottky or Mott barriers, or MOS or MIS barriers. General limitations imp...