Scanning Electron Microscope Characterization of GaP Red-Emitting Diodes

Abstract

Accurate measurements of the near-junction properties of three different red-emitting GaP p-n junction structures have been made using the scanning electron microscope (SEM). The structures consisted of similar Zn, O-doped p-type liquid-phase-epitaxial (LPE) layers grown on different Te-doped n-type substrates, which include solution-grown (SG) crystals, liquid-encapsulated Czochralski (LEC) crystals, and LPE layers grown on LEC crystals. These junctions have yielded diodes with electroluminescent efficiencies as high as 6.0, 2.0, and 4.5%, respectively. These measurements, which include minority-carrier diffusion lengths, the spatial distributions of luminescent efficiency, and the detailed properties of the space-charge region, have provided a self-consistent picture of the factors which determine electroluminescent efficiency. In this study, all of the junctions were determined to be n+-p structures which exhibit uniform red luminescent efficiencies in the p region near the junction. The differences between the structures were found to lie in the relative contributions of nonradiative recombination centers, which tend to reduce both luminescent efficiency in the p region and injection efficiency into the p region. These centers were found to be most prominent for the LEC single LPE junctions, to a lesser degree for the LEC double LPE junctions due to a buffering effect of the additional n layer, and least of all in the SG single LPE junctions. For these 6.0% SG single LPE diodes, the injection efficiencies and luminescent efficiencies were determined to be 50% and 20%, respectively, allowing for 60% external coupling efficiencies. These values are consistent with those obtained from diode electrical and electroluminescent measurements, and agree with photoluminescent measurements in the p region.

Very High Efficiency GaP Green Light Emitting Diodes

“…The measurements are made by scanning a focused electron beam across a polished surface perpendicular to the junction on a 15 • 15 rail die. The diffusion lengths are determined from the functional dependence of the induced junction current with scan distance across the junction (13). The electron beam excitation levels were also adjusted to provide carrier densities equivalent to diffusion current densities of ~1-10 A/cm 2 through a p-n junction.…”

Investigations on CMOS photodiodes using scanning electron microscopy with electron beam induced current measurements

“…From the measurements one can see that the lower the acceleration voltage is the steeper the decay is and thus the smaller the effective diffusion length in the investigated region. 13,14 One possible reason for the differences between the measurements and the simulations could be an even higher surface recombination rate than used in simulation. The comparison of the surface influence in Figure 10 indicates that the experimental surface may be of even less quality than assumed in the simulations.…”

Effect of Substrate Microdefects Due to Thermal Etching on the Near‐Junction Properties of GaP : Zn , O Grown by Liquid Phase Epitaxy

“…Scan a, taken outside of the thermal etch pit, is shown in Fig. 7 with a CL profile that is the complementary function of the BIC profile normally characteristic of a p -n junction behavior with no "dead layers" (8,9). For the scans made at the edge (scan b) and center (scan c) of the etch pit, the CL intensity has a minimum at the position of the dark ring shown in Fig.…”