Electrical properties of InAlAs/InAsxP1-x/InP composite-channel modulation-doped structures grown by solid source molecular beam epitaxy

Abstract

We report on the electrical characteristics of the two-dimensional electron gas (2DEG) formed in an InAlAs/InAsxP1-x/InP pseudomorphic composite-channel modulation-doped (MD) structure grown by solid source (arsenic and phosphorus) molecular beam epitaxy (SSMBE). The As composition, x, of strained InAsxP1-x was determined by x-ray diffraction analysis of InP/InAsxP1-x/InP multi-quantum wells (MQWs) with compositions of x=0.14 to x=0.72. As the As composition increases, the room temperature sheet resistance of InAlAs/InAsxP1-x/InP composite-channel MD structures grown over a range of As compositions decreased from 510 to 250 Ω/cm2, resulting from the greater 2DEG confinement and lower electron effective mass in the InAsxP1-x channel as x increases. The influence of growth conditions and epitaxial layer designs on the 2DEG mobility and concentration were investigated using 300 K and 77 K Hall measurements. As the exposure time of the As4 flux on the growth front of InAsxP1-x increased during growth interruptions, the 2DEG mobility, in particular the 77K mobility, was considerably degraded due to increased roughness at the InAlAs/InAsxP1-x interface. For the InAlAs/InAs0.6P0.4/InP composite-channel MD structure with a spacer thickness of 8 nm, the room temperature 2DEG mobility and density were 7200 cm2/Vs and 2.5 × 1012 cm−2, respectively. These results show the great potential of the InAlAs/InAsxP1-x/InP pseudomorphic composite-channel MD heterostructure for high frequency, power device applications.