Optoelectronic device mapping using differential imaging techniques

A mapping technique has been developed that uses differential imaging to characterize semiconductor optoelectronic devices. Although the technique was developed for examination of optical modulators, it has been extended to provide information on the uniformity and bandgap of any material through which one can transmit light. The sharpness of the bandedge, maximum absorption strength, and the film thickness determine the sensitivity of the technique for any particular application. For example, the bandedge sensitivity in 100 periods of InGaAs/GaAs multiple quantum wells was ±20 μeV and can be detected at each location in the field of view in under three minutes. This technique has been applied to modulators designed using strained layer materials for use at a 1-μm operating wavelength.