Characterization of AlGaN/GaN heterostructures grown by metalorganic chemical vapor deposition

We report the growth and characterization of high-quality AlGaN/GaN heteroj unctions by low-pressure metalorganic chemical vapor deposition. We have me asured the mobility, mu(n), and sheet charge density, n(s) of the interfaci al two-dimensional electron gas (2DEG) as a function of Al composition, sub strate orientation, and modulation doping. We have also attempted to correl ate these results with (102) X-ray diffraction linewidths and surface rough ness measured by atomic force microscopy. Interestingly, we do not find any correlation between the roughness of the wafer surface and the 2DEG concen tration or mobility Inserting a short NH3/H-2 purge immediately before init iating the AlGaN growth improves the 2DEG mobility in these AlGaN/GaN struc tures. By optimizing the growth conditions, we have achieved Al0.30Ga0.70N/ GaN heterostructures on (0001) sapphire with 2DEG mobilities in excess of m u(n) = 1300 cm(2)/Vs at 300 K and 4500 cm(2)/Vs at 100 K with n(s) similar to 9.4 x 10(12) cm(-2).