Influence of Internal Electric Field on the Recombination Dynamics of Localized Excitons in an InGaN Double-Quantum-Well Laser Diode Wafer Operated at 450 nm

Optical and structural properties of an InGaN double-quantum-well (DQW) laser diode (LD) wafer that lased at 450 nm were investigated to discuss an enormous impact of a polarization-induced electric field on the recombination dynamics in InGaN quantum structures. The quantum-well (QW) structure was shown to have the well thickness as thin as approximately 1 nm and InN molar fraction x of approximately 14%. The gross effective electric field in the QW (F _QW) was estimated to be 490kV/cm from the Franz-Keldysh oscillation (FKO) period in the electroreflectance (ER) spectrum, implying that an internal piezoelectric field (F_piz) of approximately 1.4MV/cm was cancelled by the pn junction built-in field (F_bi) and Coulomb screening due to carriers in the DQW. The magnitude of F_QW can be further weakened by applying reverse bias (V_R) on the junction; the decrease in the photoluminescence (PL) lifetime at low temperature measured under V_R was explained to be due to a recovery of electron-hole wavefunction overlap for small V_R (|V_R|<4 V), and due mainly to the tunneling escape of carriers through the barriers for larger V_R. By applying an appropriate V_R smaller than 4V, electron-hole wavefunction overlap, which had been separated vertically along the c-axis due to quantum-confined Stark effect, could be partially recovered, and then the time-resolved PL signals exhibited a less-pronounced stretched exponential decay, giving a scaling parameter (0β) of 0.85 and effective in-plane localization depth (E₀) of 40-50 meV for the spontaneous emission. These values were closer to those of much homogeneous QWs compared to those reported previously for InGaN QWs having similar InN molar fractions. The use of very thin QWs is considered to bring easier Coulomb screening of F _QW and population inversion under high excitation conditions.