Molecular beam epitaxial growth and device performance of metamorphic high electron mobility transistor structures fabricated on GaAs substrates

Abstract

Single and double pulse doped metamorphic high electron mobility transistor (MHEMT) structures have been grown on GaAs substrates by molecular beam epitaxy. A linear indium graded buffer layer was used to expand the lattice constant. Transmission electron microscopy cross sections showed planar interfaces. Threading dislocations were not observed along both cleavage directions. For a single pulse doped MHEMT structure with an ${\mathrm{In}}_{\mathrm{0.56}}{\mathrm{Ga}}_{\mathrm{0.44}}\mathrm{As}$ channel layer, the mobilities (10 030 cm²/V s at 292 K; 32 560 cm²/V s at 77 K) and sheet density ${\text{(3.2×10}}^{12} {\mathrm{cm}}^{\text{−2}})$ were nearly equivalent to values obtained for the same structure grown on an InP substrate. Secondary ion mass spectroscopy measurements of a double pulse doped structure indicated no measurable migration of the silicon doping pulses. MHEMT devices with 0.15 μm gates were fabricated, tested, and compared to GaAs pseudomorphic HEMT devices of the same geometries. Above 9 GHz, the MHEMT devices exhibited lower noise figure. From 3 to 26 GHz, the associated gain was 3 dB higher with the MHEMT devices. Also higher linearity performance was obtained with the MHEMT devices. At 4 GHz MHEMT linearity measurements yielded third order intermodulation distortion intercepts, IP3, of 36–39 dBm with linearity figure of merits of 60–90. Due to the significantly lower cost and more robustness of GaAs substrates compared to InP substrates, MHEMT technology is very promising for low cost manufacturing of low noise amplifiers.