M. V. Ramana Murty

In situ, real-time measurement of wing tilt during lateral epitaxial overgrowth of GaN

By performing in situ, real-time x-ray diffraction measurements in the metalorganic chemical-vapor deposition environment, we have directly observed the emergence and evolution of wing tilt that occurs during the lateral overgrowth of GaN from stripes patterned in a SiO2 mask. This was done by repeatedly performing line scans through the 1013 peak in the direction perpendicular to the [1010]GaN stripe direction. The wing tilt developed as soon as the wings started forming, and increased slightly thereafter to reach a value of ∼1.19° after 3600 s of growth. Upon cooldown to room temperature, the tilt increased to ∼1.36°, indicating that thermally induced stresses during cooldown have only a small effect on wing tilt. However, changes in mask density, composition, and stress state during early lateral overgrowth must be considered as possible origins of wing tilt.

Layer-by-layer growth of GaN induced by silicon

We present in situ x-ray scattering studies of surface morphology evolution during metal–organic chemical vapor deposition of GaN. Dosing the GaN(0001) surface with Si is shown to change the growth mode from step-flow to layer-by-layer over a wide temperature range. Annealing of highly doped layers causes Si to segregate to the surface, which also induces layer-by-layer growth.

In situ x-ray scattering study of PbTiO3 chemical-vapor deposition

We present in situ surface x-ray scattering measurements of PbTiO3 epitaxy by metal–organic chemical-vapor deposition. Oscillations in crystal truncation rod intensity corresponding to layer-by-layer growth are observed under a variety of growth conditions. At lower PbO overpressures, we observe a transition to step-flow growth and an increased rate of recovery after growth, indicating a higher surface mobility.

In situ studies of the effect of silicon on GaN growth modes.

Abstract We present real-time X-ray scattering studies of the influence of silicon on the homoepitaxial growth mode of GaN grown by metal-organic vapor-phase epitaxy. Both annealing of Si-doped GaN and surface dosing of GaN with disilane are shown to change the mode of subsequent growth from step-flow to layer-by-layer. By comparing the growth behavior induced by doped layers which have been annealed to that induced by surface dosing, we extract an approximate diffusion coefficient for Si in GaN of 3.5 ×10 −18 cm 2 / s at 810°C.

Investigations of Chemical Vapor Deposition of GaN Using Synchrotron Radiation

The authors apply synchrotron x-ray analysis techniques to probe the surface structure of GaN films during synthesis by metal-organic chemical vapor deposition (MOCVD). Their approach is to observe the evolution of surface structure and morphology in real time using grazing incidence x-ray scattering (GIXS). This technique combines the ability of x-rays to penetrate the chemical vapor deposition environment for in situ measurements, with the sensitivity of GIXS to atomic scale structure. In this paper they present examples from some of their studies of growth modes and surface evolution as a function of process conditions that illustrate the capabilities of synchrotron x-ray analysis during MOCVD growth. They focus on studies of the homoepitaxial growth mode, island coarsening dynamics, and effects of impurities.