Study Of Ga-droplet Surface Irradiated By In-situ UV Pulsed Laser

Semiconductor quantum structures have already been extensively researched for fabricating all kinds of opto-electronic and micro-electronics devices due to the unique optical and electrical properties.With the increasing demand for device performance,people have began to extensively adopt droplet epitaxy to prepare novel quantum structures.As we know in droplet epitaxy,the size of the metal droplet not only determines the size of the target quantum structure,but also defines the subsequent crystallization process.The temperature is the most critical factor for controlling the size of droplet.In order to obtain large droplets,the substrate temperature must increase,but high temperature will cause the droplets to etch into substrate drastically.Consequently,it makes great significances for the traditional droplet epitaxy to find a new technology,with temperature-independence,to modify the droplet size.However,most of the current studies on droplets are focusing on the crystallization process,rather than the dynamic behavior of the droplet itself.In this paper,the UV pulsed laser is used to in situ irradiate the Ga-droplet surface based on molecular beam epitaxy to achieve the secondary modification of droplet size for a controlled droplet epitaxy,the main research contents are listed as following:The first irradiation work was carried out on a high density Ga-droplet surface which was prepared at 180? and it was found: For low irradiation level,laser heating only expands droplets to make mergence among them,so in this stage,the droplet size distribution is solely shifted to the large side;for high irradiation level,laser irradiation not only causes thermal expansion but also thermal evaporation of Ga atom which makes the size-shift move to both sides.Ultimately,a special nanometal Ga-droplet of extremely broad size-distribution with width from 16 nm to 230 nm and height from 1 nm to 42 nm are successfully obtained.And the second irradiation work was carried out on a low density Ga-droplet surface which was prepared at the 300? and the results show: The coalescence was significantly suppressed due to the large gap between droplets,with the increase of pulsed laser energy,local droplet coalescence could produce the nano-holes with 2.6 nm in depth,which is much larger than the depth of three atomic layers at 180?.In addition,small Ga-droplets were also observed to form on the naked Ga As surface area where without Ga-droplet capping before the irradiation.The mass exchange between the Ga-droplet and the substrate under high temperature is more obvious and nanoholes will directly show up after only 2 minutes of annealing at 350?.