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

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9 Author(s)
Cavus, A. ; Northrop Grumman Space Technology, Redondo Beach, California 90278 ; Sandhu, R. ; Monier, C. ; Cox, C.
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InxAl1-xAs/InxGa1-xAs heterojunction bipolar transistors (HBTs) with lattice parameters ranging from 6.00 to 6.058 Å 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 6.058 Å. 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 6.00 Å. 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 0.23 μm 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 0.45 μm thick buffer layers exhibited a crosshatch pattern with a surface rms roughness of 4 nm 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 0.45 V, high current gain, low reverse junction leakage(≪1 μA), and rf peak performance in the vicinity of 150 GHz. Finally, preliminary circuits (dividers and delay chains) have been designed, fabricated, and demonstrated with the 6.00 Å HBT technology.

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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures  (Volume:24 ,  Issue: 3 )