Fabrication of periodic gallium droplets by in-situ laser interference based on MBE

In this work, the GaAs substrate was in-situ irradiated by a single-pulse of two-beam laser interference at a low temperature of 40℃. We studied the irradiated surface morphology evolution with the different pulse energies of 20mJ, 40mJ, 50mJ, 60mJ, 80mJ and 100mJ which are corresponding to sample A-F. For Sample A, the irradiation yield of Ga atoms is too limited to form metallic droplets but films with a period of about 310nm due to the low pulse energy. For Sample B, periodic bands of Ga droplets appear on the bright regions while the surface on the dark regions remains very smooth. The droplet density, average width and height are 7.5×1010/cm2, 25nm and 5.1nm. For sample C to E, as the energy rises, the average width/height of Ga droplets rise from 33nm/5.9nm, 36.7nm/8.7nm to 52.1nm/15.7nm but with the decreased density from 5.8×1010/cm2, 4×1010/cm2 to 1.7×1010/cm2. Moreover, some small Ga droplets also appear in the dark regions. Finally for sample F, when the energy becomes enough high, both the dark and bright regions generate Ga droplets of a similar size and density which is equivalent to the random growth. The resulting density is 7.4×109/cm2 and the average width/height is 63.6nm/20.2nm. Obviously, our work has provided a novel approach for fabricating periodic Ga droplets directly in MBE systems with the advantages of low-cost, high-efficiency and strong controllability which must be able to find great application prospects in droplet epitaxy of all kinds of semiconductor devices based on periodic arrays of quantum structures.