Depth distribution of traps in Au/n-GaAs Schottky diodes with embedded InAs quantum dots

Self-assembled InAs quantum dots (QDs) were grown by molecular-beam epitaxy in an n-type GaAs buffer layer, capped with an n-type GaAs layer with a thickness of 0.8 mu m. The depth distribution of the QDs-induced traps in the GaAs confining layers is investigated with low-frequency noise measurements by removing a GaAs cap layer and using Au/n-GaAs Schottky diodes as test devices. In diodes containing QDs grown from a 3-monolayer (ML) InAs coverage, the forward current noise spectra are composed of two components: a 1/f noise at frequencies below 100 Hz and a generation-recombination (g-r) noise at higher frequencies. The 1/f noise is due to the interface trap property and the g-r noise to the monoenergetic midgap traps. It is found that the density of the g-r centers increases from the surface of the GaAs cap layer to the region close to the QDs by more than one order of magnitude, whereas their density in the underlying GaAs buffer layer is lower. In diodes containing QDs grown from a 2.4-ML InAs coverage, the noise spectra are composed of two components: a 1/f noise at frequencies below 100 Hz and a shot noise at higher frequencies. The absence of the g-r noise indicates that the quality of the upper GaAs confining layer remains unchanged in the case of QDs grown from a 2.4-ML InAs coverage.