Inhomogeneities of InGaN/GaN MOVPE multi quantum wells grown with a two temperatures process studied by transmission electron microscopy

Abstract

The structural investigation of InGaN/GaN:Si multiple quantum well (MQW) samples grown by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) in a two temperatures (2T) process on high-pressure GaN mono-crystalline substrates is performed by transmission electron microscopy (TEM). A sample in which barriers and wells were grown at 780 8C is compared with another in which the barriers were deposited at 900 8C and the wells at 730 8C. For both samples the indium composition in the QWs reaches the level of about 20 at.%. The local indium composition was measured through strain measurements by digital processing from the lattice fringes images taken by TEM. Cross-sectional investigations are performed in two zone axes -[1100] and [1120] -with the use of axial and off-axis illumination. During TEM investigations the formation of ''false indium clusters '' of the size of 2-4 nm was observed for both samples just after 2 min of LaB6 electron beam illumination at 200 kV. Large lateral fluctuations of indium content in the QWs of the length of 30-130 nm were detected in 2T sample. The plan view analysis was carried out to characterize the anisotropy of the indium fluctuation inside the QWs.

Quantitative Chemical Mapping of InGaN Quantum Wells from Calibrated High-Angle Annular Dark Field Micrographs

“…Among the available nanoscale characterization techniques, transmission electron microscopy (TEM) has been extensively and successfully used to characterize InGaN (Gu et al, 2009; Kret et al, 2010; Özdöl et al, 2010; Rosenauer et al, 2011 b ; Rigutti et al, 2013). In particular, scanning transmission electron microscopy (STEM), in high-angle annular dark-field (HAADF) mode, offers chemical information through Z- contrast with a strong dependence of the signal intensity on atomic number (Crewe et al, 1970).…”

Impact of Thin LT-GaN Cap Layers on the Structural and Compositional Quality of MOVPE Grown InGaN Quantum Wells Investigated by TEM

“…In sample B the QWs are mostly discontinuous with areas of high indium concentration followed by areas where the indium percentage is very low or zero. As demonstrated in [4], where a plane view of sample A is shown, the inhomogeneities are in fact stripe like InGaN features with a finite width. In the cross-section the stripes appear as InGaN islands (Fig.…”

“…In a previous work [4] we reported the effects of a two--temperature process on InGaN/GaN QWs with 4.5 nm nominal thickness (sample A). A degradation causing a reduction of the thickness of the InGaN layers due to indium desorption was observed.…”

Effect of the barrier growth mode on the luminescence and conductivity micron scale uniformity of InGaN light emitting diodes

“…The first is the so called two-temperature (2 T) [3][4][5] approach, where the temperature is ramped up and down between around 900 C for the barriers and 750 C for the wells. This is expected to improve the crystal quality of the GaN, but results in an increased indium loss from the QW.…”