Carrier Diffusion in GaN: A Cathodoluminescence Study. I. Temperature-Dependent Generation Volume

The determination of the carrier diffusion length of semiconductors such as GaN and GaAs by cathodoluminescence imaging requires accurate knowledge about the spatial distribution of generated carriers. To obtain the lateral distribution of generated carriers for sample temperatures between 10 and 300 K, we utilize cathodoluminescence intensity profiles measured across single quantum wells embedded in thick GaN and GaAs layers. Thin (Al,Ga)N and (Al,Ga)As barriers respectively prevent carriers diffusing in the GaN and GaAs layers to reach the well, which would broaden the profiles. The experimental cathodoluminescence profiles are found to be systematically wider than the energy loss distributions calculated by means of the Monte Carlo program CASINO, with the width monotonically increasing with decreasing temperature. This effect is observed for both GaN and GaAs and becomes more pronounced for higher acceleration voltages. We discuss this phenomenon in terms of both the electron-phonon interaction controlling the energy relaxation of hot carriers and the shape of the initial carrier distribution. Finally, we present a phenomenological approach to simulate the carrier generation volume that can be used for the investigation of the temperature dependence of carrier diffusion.

Automated summary

This study investigates the accurate knowledge about the spatial distribution of generated carriers needed for determining the carrier diffusion length of semiconductors such as GaN and GaAs through cathodoluminescence imaging. By measuring the cathodoluminescence intensity profiles across single quantum wells embedded in thick GaN and GaAs layers, the lateral distribution of generated carriers between sample temperatures of 10 and 300 K is obtained. The experimental cathodoluminescence profiles are observed to be wider than the calculated energy loss distributions, with the width increasing monotonically as the temperature decreases. This phenomenon is present in both GaN and GaAs and becomes more pronounced at higher acceleration voltages. The electron-phonon interaction and the shape of the initial carrier distribution are discussed as possible factors influencing this effect. Finally, a phenomenological approach is presented for simulating the carrier generation volume and investigating the temperature dependence of carrier diffusion.