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(a) Schematic energy band diagram near the sample surface. The inset shows the detailed valence band lineup of the InGaN/AlGaN superlattice layers. (b) Schematic of the sample structure used in the experiment. Also shown is the metal contact required for the electrochemical etching. (c)HR-TEM image of the GaN epilayer structure grown by MO-CVD.
Optical microscope images of the samples etched at various reverse-bias voltages: (a) 10 V, (b) 15 V, (c) 20 V, and (d) 25 V. (e) Cross sectional SEM image of a sample etched at the applied voltage of 20 V.
Optical microscope images for a set of samples etched for different durations: (a) 5 min, (b) 10 min, (c) 20 min, and (d) 30 min. Reverse bias voltage was kept the same for all samples at 20 V. (e) Plot of the lateral etch depth versus etch time.
CCD camera images of a 5 × 5 array pattern of square mesas containing MQWs: (a) before and (b) after the electrochemical lift-off. Optical microscope images of the patterned mesas: (c) before and (d) after the electrochemical lift-off. It should be noted that (b) and (d) were taken after the SiO2 hard mask layer was removed in a buffered oxide etchant.
(a) Schematic of the μ-PL measurement setup. (b) μ-PL spectra of unetched (thin black line) and etched (thick red line) samples. CCD images, taken while illuminated broadly by a 325 nm laser source, for (c) etched and (d) unetched samples.
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