Mapping nonlinearities over the active regions of semiconductor devices

A laser scanner employing a modulated low-power 0.633- µm He-Ne laser has been used in a nondamaging manner to locate portions of a silicon bipolar UHF transistor which electrically behave in a nonlinear manner at a signal frequency of 470 MHz. In effect, the method uses the device scanned as a frequency converter to produce an IF output for a display screen whenever the laser spot is incident on nonlinear regions.