Luminescence of laterally ordered Ge islands along 〈100〉 directions

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Abstract
The optical properties of coherently strained, self-ordered Ge islands are analyzed in connection with their size distribution. The ordering was achieved by depositing Ge on Si mesas oriented parallel to 〈100〉 directions and grown by selective epitaxy on Si(001) using low pressure chemical vapor deposition. The spontaneous ordered nucleation of Ge islands along mesa edges is driven by the presence of tensile strain at the periphery of the mesas. All photoluminescence peaks of the islands as well as of the wetting layer are well resolved. The emission peaks of ordered islands could be separated from the emission of randomly distributed islands on the (001) plane by varying the width of the straight mesa lines. The peaks of ordered islands are narrower than from random islands in agreement with the atomic force microscopy analysis. This effect is due to the strong island–island interaction in the one-dimensional row. The emission is governed at low temperature by hole transfer from the wetting layer to the islands, and at higher temperature by hole transfer from the islands to the wetting layer.