The development of optical communication systems, various optical devices and other optical systems has created the need for various new devices, modifications of existing devices, and processes for making such devices. A particularly important class of optical devices are those involving use of various compound semiconductors. Typical examples of such devices are light emitting diodes, optical detectors, and semiconductor lasers. Often, it is required to form various geometrical shapes on the surface of the compound semiconductor which must be of optical quality. A typical example is the formation of a lens on the surface of a light emitting diode. The lens is used to collect radiation given off isotropically inside the light emitting diode and concentrate it in a particular direction. A typical example is concentration of light from a light emitting diode into an optical fiber in an optical communication system.
In the production of many optical devices, batch processing is used where many devices are produced simultaneously on one semiconductor wafer. Typically, in the production of light emitting diodes, more than about 20 devices are made on a single wafer. Processing is carried out simultaneously on all the devices. In producing geometrical shapes of optical quality, it is highly desirable economically that it be done on all the devices simultaneously without attention to individual diodes. In other words, it is desirable to have an etching procedure which can etch precise geometrical shapes and yield surfaces of optical quality which will transmit or reflect radiation without excessive scattering.
A photoelectrochemical etching procedure for p-type gallium arsenide has been described in the literature (see Applied Physics Letters, 39(1), page 76 (1981)) but this procedure applies only to p-type compound semiconductors.