Using the meltback and regrowth, new fabrication method of micro-lens is developed. It is possible to control the lens parameters by meltback time, mask window diameter, Al/Ga weight ratio and others. From the depth and time relation in the meltback, it becomes easy to control the etch depth by the aluminum weight increase in gallium melt. The meltback etch depth is proportional to the time linearly at initial contact and changed to square-root dependence.
(111) crystallographic planes in parallel to the [110] directions are clearly demonstrated. It is possible to reduce the planes as well as the gallium carry-over by the aluminum to gallium weight ratio. The lensed LED's with the single hetero and double-hetero structure were fabricated. The efficiency of lensed DH LED is three times higher than the flat surface emitting LED. In the near field pattern of the lensed LED, clear extent of pattern was observed. Slight deviations from the ideal hemispheric structure was demonstrated because of the anisotropic meltback phenomena.
The process is simple and compatible with LPE and other GaAs technologies. Using optical lithography, two dimensional array of optical devices are possible to obtain. There is no chemical or gaseous contamination at the interface during the crystal regrowth for the substrate is cleaned free of any oxide by meltback. The advantages of the structure include high efficiency, clear near field pattern and easy integration in the lensed LED.
