Multiple characterizations of the final layer of the buffer as a function of the phosphine partial pressure. (a) RMS roughness from 100 μm × 100 μm area, measured by AFM. (b) Threading defect density measured from cathodoluminesence measurements. (c) FWHM of the XRD RSM peaks from (110) incidence and ω rotation. (d) Stress-thickness product at the end of growth, and (e) residual strain of the overshoot buffer, both measured at growth temperature by in situ wafer curvature.
An example AFM image showing the crosshatch roughness that develops during the course of the growth of a compositionally graded buffer. This sample was grown using a phosphine partial pressure of 5.5 Torr and at a growth rate of 4.4 μm/h.
Cathodoluminescence intensity maps of samples with a growth rate of 4.4 μm/h and phosphine partial pressures of (a) 2.8 Torr and (b) 9.5 Torr. The brightness of the image corresponds with the intensity of the luminescence at that point. Threading dislocations are dark spots in the image, some examples of which are identified by overlaid green circles.
Stress-thickness product throughout growth of GaInP compositionally graded buffers. The three growths shown have identical structure, shown in the above diagram, but varied phosphine partial pressure throughout growth. The green vertical lines separate the various layers of the CGB.
Characterizations of the final layer of the buffer as a function of the growth rate. (a) RMS roughness from 100 μm × 100 μm area, measured by AFM. (b) Threading defect density measured from cathodoluminesence measurements.
(a) Light J-V curve of a mismatched solar cell grown using conditions that minimize roughness. (b) Internal quantum efficiency of the same mismatched solar cell. The internal quantum efficiency compensates for reflectance and grid obscuration.
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