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/.
Ionization by drift and ambipolar electric fields in electronegative capacitive radio frequency plasmas.
Unlike α- and γ-mode operation, electrons accelerated by strong drift and ambipolar electric fields in the plasma bulk and at the sheath edges are found to dominate the ionization in strongly electronegative discharges. These fields are caused by a low bulk conductivity and local maxima of the electron density at the sheath edges, respectively. This drift-ambipolar mode is investigated by kinetic particle simulations, experimental phase-resolved optical emission spectroscopy, and an analytical model in CF(4). Mode transitions induced by voltage and pressure variations are studied.