Development of 6.00Å graded metamorphic buffer layers and high performance In0.86Al0.14As∕In0.86Ga0.14As heterojunction bipolar transistor devices

Abstract

In x Al 1 − x As ∕ In x Ga 1 − x As heterojunction bipolar transistors (HBTs) with lattice parameters ranging from 6.00to6.058Å employing the use of narrow band gap InxGa1−xAs base epitaxial layers toward InAs (0.86<Xln<1) allows for the development of high speed digital and mixed signal circuits to perform at half the power required for conventional group III-V-based HBT device technologies. However, one of the key challenges inhibiting the development of low power narrow band gap HBT device circuits is the absence of semi-insulating (SI) substrates with lattice parameters towards 6.058Å. Therefore, a metamorphic InxAl1−xAs (0.52<Xln<0.86) graded buffer layer (GBL) grown on InP by molecular beam epitaxy was investigated as a means to enable a SI template with a lattice parameter of 6.00Å. The metamorphic InxAl1−xAs GBL thickness is desired to be less than a micron in order for this approach to be compatible with the aggressive design rules of high-density transistor circuits. In this study, In0.86Al0.14As∕In0.86Ga0.14As double heterojunction bipolar transistor devices were grown on 0.90, 0.45, and 0.23μm thick InxAl1−xAs GBLs to assess the role of buffer layer thickness on both defect formation and device performance. The material characterization results for the 0.90 and 0.45μm thick buffer layers exhibited a crosshatch pattern with a surface rms roughness of 4nm and threading dislocation densities of ∼106cm−2. Excellent dc and rf characteristics from metamorphic HBT devices with submicron emitter widths were observed with low turn-on voltage of 0.45V, high current gain, low reverse junction leakage(<1μA), and rf peak performance in the vicinity of 150GHz. Finally, preliminary circuits (dividers and delay chains) have been designed, fabricated, and demonstrated with the 6.00Å HBT technology.