The Use of Low Temperature AlInAs and GalnAs Lattice Matched to InP in the Fabrication of HBTs and HEMTs
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THE USE OF LOW TEMPERATURE AlInAs AND GalnAs LATTICE MATCHED TO InP IN THE FABRICATION OF HBTs AND HEMTs R.A. METZGER, A.S. BROWN, R.G. WILSON, T. LIU, W.E. STANCHINA, L.D. NGUYEN, A.E. SCHMITZ, L.G. McCRAY, AND J.A. HENIGE Hughes Research Laboratories, 3011 Malibu Canyon Rd., Malibu CA 90265
ABSTRACT AllnAs and GalnAs lattice matched to InP and grown by MBE over a temperature range of
200 to 350*C (normal growth temperature of 500'C) has been used to enhance the device performance of inverted (where the donor layer lies below the channel) High Electron Mobility Transistors (HEMTs) and Heterojunction Bipolar Transistors (HBTs), respectively. We will show that an AlInAs spacer grown over a temperature range of 300 to 350'C and inserted between the AlInAs donor layer and GaInAs channel significantly reduces Si movement from the donor layer into the channel. This produces an inverted HEMT with a channel charge of 3.0x1012 cm-2 and mobility of 9131 cm 2/V-s, as compared to the same HEMT with a spacer grown at 500 *Cresulting in a channel charge of 2.3x1012 cm- 2 and mobility of 4655 cm2/V-s. We will also show that a GaInAs spacer grown over a temperature range of 300 to 350*C and inserted between the AlInAs emitter and GalnAs base of an npn HBT significantly reduces Be movement from the base into the emitter, thereby allowing higher Be base dopings (up to Ix10 20 cm- 3) confined to 500 A base widths, resulting in an AlInAs/GaInAs HBT with an fmax of 73 GHz and ft of 110 GHz. INTRODUCTION Al0.481n0 .52 As and Ga0 .471n0 .53As lattice matched to InP are extremely useful for high-speed electronic and optical devices [1-2]. Device applications often require high resistivity, low lifetime material to act as buffers for electrical isolation and reduction of backgating and sidegating [3-6]. It has been demonstrated that these characteristics can be obtained using lattice matched materials grown at temperatures substantially below those of normal growth conditions in which excess As in quantities of 1-2% are present. This growth regime is often referred to as Low Temperature (LT) growth [3-6]. There is, however, an intermediate growth regime between that of normal growth (500 to 600'C) and LT growth (below 200'C) in which there is little to no excess As, but in which the movement of dopant atoms has been significantly reduced, compared with material grown at normal temperature [7-11]. We have utilized this intermediate growth regime to produce AlInAs and GaInAs that inhibits the movement of Si and Be, but is not so heavily defected or the lifetime so degraded that it becomes unsuitable for use in the active regions of HEMTs and HBTs. EXPERIMENTAL The epitaxial layers were grown in Perkin Elmer PHI-430 and Riber 2300 MBE systems. The substrate temperature was referenced to the (2x4) to (4x2) surface transition as determined by Reflected High Energy Electron Diffraction (RHEED) patterns that occurs upon heating the InP substrate in an As 4 beam before growth is initiated. For these experiments, using an As4 beam equivalent pre
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