Low Turn-on Voltage InGaP / GaAsSb / GaAs DHBT Grown by MOCVD
In this work, an InGaP/GaAsSb/GaAs DHBT with carbon doping up to 4E19/cm GaAsSb base was studied. A current gain of 115 at the collector current density of 25KA/cm2 was achieved for the Rbs of about 530ohm/sq. Over 100mV turn-on voltage and knee voltage reduction and 2/3 offset voltage were obtained for the GaAsSb based HBT compared with the standard InGaP/GaAs SHBT. The DC gain of the device is less temperature dependence (the DC gain variation is less than 3% for the temperature range from 25 degree C to 100 degree C.) due to the larger valence band discontinuity between InGaP emitter and GaAsSb base, compare with the standard InGaP/GaAs SHBT. These results indicate that GaAsSb is a great choice for the base material of a low turn-on voltage HBT.
A miniature 44% efficiency GaAs HBT power amplifier MMIC for the W-CDMA application
This paper presents a new linearizing circuit, which gives high power-added-efficiency with low distortion for the W-CDMA application. Since this linearizing circuit is realized by adding a small transistor, a resistor and a capacitor to the bias circuit, the required chip size is small enough and no extra loss in the signal path occurs. The designed 1.95 GHz two-stage power amplifier using HBTs shows 44% power-added-efficiency (PAE), 27.6 dBm output power and 21 dB gain with -37 dBc adjacent channel leakage power ratio (ACLR), at a supply voltage of 3.4 V. In contrast, the conventional power amplifier without linearizer shows 3 dB degradation in ACLR under the same conditions described above. Also, the chip size, which directly affects cost, is less than 1 mm/sup 2/.
High performance Al/sub 0.35/Ga/sub 0.65/As/GaAs HBT's
AlGaAs emitter heterojunction bipolar transistors (HBTs) are demonstrated to have excellent dc and RF properties comparable to InGaP/GaAs HBTs by increasing the Al composition. Al/sub 0.35/Ga/sub 0.65/As/GaAs HBTs exhibit very high dc current gain at all bias levels, exceeding 140 at 25 A/cm/sup 2/ and reaching a maximum of 210 at 26 kA/cm/sup 2/ (L=1.4 /spl mu/m/spl times/3 /spl mu/m, R/sub sb/=330 /spl Omega///spl square/). The temperature dependence of the peak dc current gain is also significantly improved by increasing the AlGaAs mole fraction of the emitter. Device analysis suggests that a larger emitter energy gap contributes to the improved device performance by both lowering space charge recombination and increasing the barrier to reverse hole injection.