Modeling photocurrent spectra of high-indium-content InGaN disk-in-wire photodiode on silicon substrate

This work reports comprehensive theoretical modeling of photocurrent spectra generated by an In_0.91Ga_0.09N/ In_0.4Ga_0.6N disk-in-wire photodiode. The strain distribution is calculated by the valence-force-field model, while a realistic band structure of the In_xGa_1−xN/In_yGa_1−yN heterostructure is incorporated using an eight-band effective bond-orbital model with spin–orbit coupling neglected. The electrostatic potential is obtained from a self-consistent calculation employing the non-equilibrium Green's function method. With the strain distribution and band profile determined, a multi-band transfer-matrix method is used to calculate the tunneling coefficients of optically-pumped carriers in the absorbing region. The photocurrent spectra contributed by both single-photon absorption and two-photon absorption (TPA) are calculated. The absorption coefficient is weighted by the carrier tunneling rate and the photon density-of-states (DOS) in the optical cavity formed in the nanowire region to produce the photocurrent. The calculated photocurrent spectra is in good agreement with experimental data, while physical mechanisms for the observed prominent peaks are identified and investigated. We found a dominant influence of the photon DOS near k_||=0, causing an enhancement of photocurrent at certain cut-off energies associated with resonance modes in the graded-index waveguide. The main features of photocurrent spectra are determined by the TPA absorption, while the peak positions depend heavily on the polarization of photon.