Effect of carrier gas and substrate misorientation on the structural and optical properties of m-plane InGaN/GaN light-emitting diodes

The properties of Si-doped GaN (GaN:Si) thin films and InGaN/GaN light-emitting diodes (LEDs) grown by metalorganic chemical vapor deposition on free-standing {1 0 1¯ 0} m-plane GaN substrates were investigated with regard to carrier gas and substrate misorientation toward the [0 0 0 1¯] c^- direction. The surface morphology of the GaN:Si thin films and the LEDs was found to be strongly dependent on the choice of carrier gas and substrate misorientation. Growth of GaN:Si thin films on nominally on-axis substrates produced surfaces with a high density of four-sided pyramidal hillocks, regardless of the composition of the carrier gas. In contrast, growth of GaN:Si thin films on substrates with misorientation angles greater than 0.7° yielded moderately to severely faceted surfaces when grown with H ₂ as the carrier gas and atomically smooth surfaces when grown with N ₂ as the carrier gas. Although the surface morphology varied significantly with substrate misorientation, the average indium mole fraction in the InGaN-based quantum wells, the output power of the LEDs, the electroluminescence (EL) peak wavelength, and the EL linewidth showed little dependence on substrate misorientation. Substrates with misorientation angles of about 1° were successfully used to grow LEDs with improved surface morphology but similar optical properties, compared to LEDs grown on nominally on-axis substrates.