A series of GaN/Al0.65Ga0.35N multi quantum wells (MQWs) with varying QW width have been investigated. Uncapped MQWs exhibit long microcracks (μ-cracks) and short nano-grooves. Significant modification of the strain in the MQW is observed as it approaches a μ-crack, representing a change from unstrained QWs with strained barriers, to compressively-strained QWs with slightly relaxed barriers. Good agreement between experimental and calculated values of MQW emission are achieved for both strain configurations by considering only field sharing and the piezoelectric effect as a source of electric field in the QWs. The field sharing arises from a redistribution of free charge in the MQW stack as a result of equalisation of the Fermi level on both sides of the MQW.
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Norman et al. (1999) studied this question.