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.
Temperature-dependent valence band offset and band-gap energies of pseudomorphic GaAsSb on GaAs
The band-gap (Egp) and valence band offset (ΔEv) energies of pseudomorphic GaAsSb layers on GaAs substrate are determined from temperature-dependent photoluminescence measurements on GaAsSb/GaAs and GaAsSb/GaAlAs quantum wells grown by molecular beam epitaxy. A clear evidence of staggered type-II band alignment of GaAsSb relative to GaAs and a value of 1.05 for the valence band offset ratio (Qv) are proposed. Finally, through a detailed comparison of these values with those published previously, we have shown that the scatter in Qv found in the literature (<1 to 2.1) is closely dependent on the exact determination of Egp. Particularly, we have shown that the strain dependence of the deformation potential is important in the calculation of the strain energy contribution to Egp.
Growth and properties of liquid‐phase epitaxial GaAs1−xSbx
A detailed study is presented of the Ga‐As‐Sb ternary phase diagram. Liquidus temperatures have been measured between 700 and 900 °C by direct observation of the solutions, and layers then grown epitaxially on GaAs substrates. The nonequilibrium effect of constitutional supercooling on the compositions of the grown layers is investigated. Solidus compositions, from layers slowly grown to minimize this effect, are used together with the liquidus data to fit a calculated phase diagram. These results lead to the conclusion that GaAs1−xSbx is a borderline case between miscible and immiscible solid solutions. An accurate determination of the ternary band gap has been made as a function of composition over the range 0⩽x⩽0.2. The room‐temperature electrical properties of undoped, Te‐doped (n‐type), and Ge‐doped (p‐type) epilayers have also been determined.