CLUSTERING NANOSTRUCTURES AND OPTICAL CHARACTERISTICS IN INGAN/GAN QUANTUM-WELL STRUCTURES WITH SILICON DOPING
Journal
III-Nitride: Semiconductor Materials
ISBN
9781860949036
Date Issued
2006-01-01
Author(s)
Abstract
The results of photoluminescence (PL), detection-energy-dependent photoluminescence excitation, excitation-energy-dependent photoluminescence, amplified spontaneous emission (ASE), cathodoluminescence (CL) and strain state analysis (SSA) of three InGaN/GaN quantum-well (QW) samples with un-doped, well-doped, and barrier-doped conditions are compared for understanding the silicon doping effects on nanostructure and photon emission mechanism. Based on the SSA and CL images, a nanostructure model is built for describing the potential fluctuation differences between the three samples. In the barrier-doped sample, strongly clustering nanostructures with individual steep potential minima, which generate significant quantum confinement effects, are assumed. In the undoped and well-doped samples, relatively weaker composition fluctuations, in which carriers relax through a cascading process, are proposed. Between the undoped and well-doped samples, the potential fluctuation in the well-doped sample is relatively steeper such that a certain extent of quantum confinement existed. Such variations in nanostructure result in different carrier transport processes between the coexistent quantum dot and quantum well states, which well explain the PL, DEDPLE, EEDPL, ASE, and CL observations. In particular, the PL results provide us clues for speculating that the S-shape behavior of PL peak position is dominated by the quantum-confined Stark effect (QCSE) in an undoped InGaN/GaN QW structure. However, carrier localization is more effective in blue-shifting luminescence and improving radiative efficiency of a sample, when compared with the relaxation of QCSE. Also, the ASE results show the temperaturedependent evolution of gain spectrum due to the liquidation of thermalized carriers. Different nanostructures result in different spectral variation trends.
Type
book part