GalnN Quantum Wells Effect of Phase Separation on Lasing

It has been proposed recently that phase separation of GalnN into In-rich and Ga-rich phases has profound consequences on the optical properties and on the lasing properties of GalnN/GaN/AlGaN quantum well heterostructures [1,2]. The nanoscale compositional fluctuations resulting from phase separation are believed to lead not only to exciton localisation [2] but even to a quantum-dot-like behaviour [3], A more detailed discussion of the microscopic aspects of phase separation is given elsewhere in this volume. 

Theoretically, ideal quantum dot structures should possess superior lasing properties compared to higher dimensional heterostructures [4], Therefore, the idea of natural quantum-dot-like structures in GalnN/GaN/AlGaN quantum wells was quite attractive. 

Before discussing the experimental evidence, it is worthwhile to consider lasing-related properties of quantum dots from a fundamental point of view. The theoretical description of the optical gain in bulk and quantum well semiconductors is discussed in Datareview C5.3. 

Ideal semiconductor quantum dot structures should exhibit a delta-function-like (atomic-like) density-of-states for both electrons mid holes [4], Optical excitations in such structures are excitonic in nature, since an electron mid a hole confined in a quantum dot necessarily interact via their Coulomb interaction mid, therefore, form mi exciton. Consequently, a single electron-hole pair in a quantum dot corresponds to mi exciton, whereas doubly occupied electron and hole states (both spin states) correspond to a biexciton. Since the Coulomb interaction of the particles is inevitable, it makes no sense to distinguish between excitons mid free electrons mid holes within a quantum dot. Optical gain 

For thick quantum wells (no significant quantisation) the shape of the optical gain spectra can be well described by a conventional band-to-band transition model [10], At least qualitatively, the same is true for thinner single and multiple quantum wells. However, the shape of the gain spectra alone cannot be used to decide on the transition mechanism. 

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C2.1 GalnN quantum wells composition pulling effect C2.2 GalnN quantum wells microstructure C2.3 GalnN quantum wells optical properties C2.4 GalnN quantum wells effect of phase separation on lasing... 

C2.4 GalnN quantum wells effect of phase separation on lasing... 

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