Crossover Energy Where Cathodoluminescence Becomes Comparable to Electroluminescence in p-Type GaAs Observed by Injecting Tunneling Electrons

Using a conductive and transparent tip, which can bear higher bias voltages than a conventional scanning tunneling microscopy (STM) metal tip, for injecting tunneling electrons, we successfully obtained the dependence of luminescence intensity on excitation energy up to 7 eV for p-type GaAs. We found a threshold energy at 4.9 eV above which the luminescence intensity substantially increases. The increase is attributable to cathodoluminescence due to the recombination of electrons and holes created by impact ionization (I.I.). The present result experimentally supports the simulation result predicting that there is no clear-cut transition, but a soft crossover, in the energy dependence of I.I. rate.