Shou-Kong Fan

Temperature dependences of current gains in GaInP/GaAs and AlGaAs/GaAs heterojunction bipolar transistors

The temperature dependences of current gain are investigated for both GaInP/GaAs and AlGaAs/GaAs heterojunction bipolar transistors (HBTs). Measured results indicate that for GaInP/GaAs HBTs the current gain at collector current densities >0.1 A/cm/sup 2/ remains nearly constant, independent of the substrate temperature for AlGaAs/GaAs HBTs. These current gain characteristics are examined, and the origin of the difference is attributed to the difference of the valence-band discontinuities in the base-emitter heterojunctions of the two HBTs. >

Near-ideal I-V characteristics of GaInP/GaAs heterojunction bipolar transistors

GaInP/GaAs heterojunction bipolar transistors (HBTs) have been fabricated and these devices exhibit near-ideal I-V characteristics with very small magnitudes of the base-emitter junction space-charge recombination current. Measured current gains in both 6- mu m*6- mu m and 100- mu m*100- mu m devices remain constant for five decades of collector current and are greater than unity at ultrasmall current densities on the order of 1*10/sup -6/ A/cm/sup 2/. For the 6- mu m*6- mu m device, the current gain reaches a high value of 190 at higher current levels. These device characteristics are also compared to published data of an abrupt AlGaAs/GaAs HBT having a base layer with similar doping level and thickness.<<ETX>>

Microwave performance of a self-aligned GaInP/GaAs heterojunction bipolar transistor

The microwave performance of a self-aligned GaInP/GaAs heterojunction bipolar transistor (HBT) is presented. At an operating current density of 2.08*10/sup 4/ A/cm/sup 2/, the measured cutoff frequency is 50 GHz and the maximum oscillation frequency extrapolated from measured unilateral gain and the maximum available gain are 116 and 81 GHz, respectively, all using 20-dB/decade slopes. These results are compared with other reported high-frequency performances of GaInP HBTs. In addition, these results are compared with AlGaAs/GaAs HBTs having a similar device structure.<<ETX>>

Current transport mechanism in GaInP/GaAs heterojunction bipolar transistors

GaInP/GaAs heterojunction bipolar transistors (HBTs) and both graded and abrupt AlGaAs/GaAs HBTs were fabricated. A total of 20 wafers were analyzed. Comparisons of the experimental results establish that the dominant carrier transport mechanism in GaInP/GaAs HBTs is the carrier diffusion through the base layer. This suggests that the conduction-band barrier across the GaInP/GaAs emitter-base junction is so small that the barrier spike does not affect the carrier transport. This result differs from other published results which, by studying device structures other than HBTs, determined the conduction band barrier to be as large as approximately 50% of the bandgap difference. The findings of the present investigation, however, agree well with another published work which also examined an HBT structure. The difference between these works is discussed. >

Extrinsic base surface passivation in GaInP/GaAs heterojunction bipolar transistors

The authors demonstrate excellent passivation of the extrinsic base surfaces in GaInP/GaAs heterojunction bipolar transistors (HBTs) having small emitter areas. Passivated devices with an area as small as 4*20 mu m/sup 2/ exhibit the highest reported current gain value of 2690 for GaInP/GaAs HBTs, while unpassivated 4*20- mu m/sup 2/ devices exhibit a current gain of only 500. Measured current gains as a function of collector current density are almost identical for devices with varying emitter widths of 4, 6, 8, 12, 16, and 100 mu m. The current gains are also nearly identical for devices with varying passivation ledge widths of 1, 2, 3, and 6 mu m. These results are contrasted with those of a previously published study reporting surface passivation for a GaInP/GaAs HBT with a large emitter area.<<ETX>>

Observation of resonant tunneling at room temperature in GaInP/GaAs/GaInP double-heterojunction bipolar transistor

Negative differential resistance (NDR) has been observed at room temperature in GaInP/GaAs double-heterojunction bipolar transistors (DHBTs). Both the common-emitter and common-base current-voltage characteristics and their magnetic field dependence have been studied to confirm that the observed NDR is due to resonant tunneling. The collector-base voltages at which the collector current resonances occur are calculated and are consistent with the measured values. The devices exhibit an offset voltage of 57 mV and saturation voltage of >

X-band GaInP/GaAs power heterojunction bipolar transistor

The large-signal performance of GaInP/GaAs HBTs (heterojunction bipolar transistors) at X-band is reported on. A CW (continuous wave) output power of 1.0 W is obtained from a GaInP/GaAs HBT consisting of ten 2- mu m*30- mu m emitter fingers, corresponding to a powder density of 33.3 W/mm. The associated power gain is 5 dB and the power-added efficiency is 40%. In addition, a record-high f/sub T/ of 50 GHz and f/sub max/ of 116 GHz are measured for a two-finger HBT. These results compare favorably with those measured for AlGaAs/GaAs HBTs, demonstrating that GaInP/GaAs HBTs are suitable for microwave power applications.<<ETX>>