Overcoming Difficulties in Photoreflectance Measurements on Product HBTs


E. M. Rehder, P. Rice, K. S. Stevens, C. R. Lutz


Kopin Corporation 695 Myles Standish Blvd. Taunton, MA  02780,  erehder@kopin.com 508-824-6696



Keywords: heterojunction bipolar transistor, hbt, photoreflectance, non-destructive



      Photoreflectance (PR) is an optical measurement technique used to study material properties and device structures.  It is uniquely able to non-destructively measure electric fields within devices.  Some device structures such as HBTs have a rough highly doped InGaAs surface layer.  In some cases the surface roughness is sufficient to produce light scattering that impedes optical measurements such as PR.  We have developed a new measurement configuration separating the pump laser, which causes the light scattering, from the probe laser.  Rapid, non-destructive measurements of the emitter and collector depletion regions are possible with this configuration on product wafers with rough surface layers


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