Inverted pseudomorphic high electron mobility heterostructures by atmospheric pressure metalorganic chemical vapor deposition

Abstract

Inverted pseudomorphic high electron mobility transistor (HEMT) and inverted HEMT heterostructures are demonstrated by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) for the first time and characterized by transmission electron microscopy (TEM), variable temperature Hall effect, and Shubnikov–de Haas measurements. TEM micrographs of both structures show distinct and sharp heterojunction interfaces without indications of interface roughness at the AlGaAs/channel layer interface. Variable temperature Hall effect measurements reveal a monotonic increase in mobility as the temperature is lowered. For the inverted HEMT, the mobility at 15 K is 90 000 cm2/V s with a sheet density of 8.2×1011 cm−2. The mobility of the inverted pseudomorphic HEMT at 15 K is 73 000 cm2/V s with a sheet density of 1.5×1012 cm−2. Shubnikov–de Haas measurements at 4.2 K in magnetic fields up to 18.5 T show clear magnetoresistance oscillations and plateaus in the quantum Hall effect confirming the existence of a two-dimensional electron gas. Fast Fourier power transform of the magnetoresistance versus magnetic field shows two subband levels with a total sheet density of 8.7×1011 cm−2 for the inverted HEMT and a total sheet density of 1.55×1012 cm−2 for the inverted pseudomorphic HEMT in close agreement to the variable temperature Hall effect measurement results.