Anomalous deep-level transients related to quantum well piezoelectric fields inInyGa1−yN∕GaN-heterostructure light-emitting diodes

Abstract

The anomalous inversion of capacitance transients was observed during deep level transient spectroscopy characterization of $\mathrm{In}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ based blue light-emitting diodes. Deep level C $({E}_{C}\ensuremath{-}{E}_{T}=0.25\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$, a majority carrier trap related to isolated point defects, has a negative transient when the bias stimulates it only in the bulk region and has a positive transient when the filling pulse is such that the quantum well (QW) region is probed. We explain this observation by a model based on the confining effects of QW piezoelectric fields on the charge emitted by deep levels. Instead of being collected by the junction, this charge is rearranged in conduction band states of the multi-QW region, shifting its center of mass toward the bulk. We measured the strength of piezoelectric fields $(2.3\phantom{\rule{0.3em}{0ex}}\mathrm{MV}∕\mathrm{cm})$ and the QW In fraction $(x=0.15)$ by means of photocurrent spectroscopy, and we tested the accuracy of our model by comparing a Schr\odinger-Poisson simulation with our experimental data, finding substantial agreement.