Localized excitons in an In0.06Ga0.94N multiple-quantum-well laser diode lased at 400 nm

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Abstract
An InGaN multiple-quantum-well laser diode wafer that lased at 400 nm was shown to have InN mole fraction x of only 6% and 2% in the wells and barriers, respectively. The Stokes-like shift (SS) and localization depth E0 were estimated to be 49 and 35 meV at 300 K although the compositional fluctuation in the well was as small as 1% or less. Since the well thickness fluctuation is insufficient to reproduce the SS or E0, the quantum-well exciton localization is considered to be an intrinsic phenomenon in InGaN, which is due to the large band-gap bowing and In clustering. The spontaneous emission was thus assigned as being due to the recombination of excitons localized at the exponential tail-type potential minima in the density of states. However, shallow and low-density localized states are leveled by injecting high-density carriers under the lasing conditions.