Liquid Contact Luminescence from Semiconductor Laser Materials

Abstract

Semiconductor diode lasers are now widely used in many applications such as optical memories (e.g. compact-disk players) and fiber-optic communications. Recently, we discovered that a liquid contact made to standard diode laser material can be used to obtain light emission resulting from electron-hole recombination in the "active" layer buried in the multilayer epitaxial structure. Since the active layer is responsible for light amplification in diode lasers made from such material, this liquid contact luminescence phenomenon has potential as a new type of diode laser material evaluation technique. In addition, since the efficiency of the light emission process can be high, the liquid contact luminescence phenomenon has the potential for use as a new type of flat panel display (FPD). vii Historically, the liquid contact luminescence phenomenon was discovered during the course of experiments involving pulsed anodic oxidation (anodization) of semiconductor laser materials in liquid electrolytes. When observed in the time domain, we found that the light was emitted, with long delays, after the termination of the voltage pulse. The complex relationship between oxide thickness, light emission intensity, and turn-on delay is described. When the drive current direction is reversed from that used in pulsed anodization, the material is not anodized and light is emitted continuously from the active layer inside the semiconductor material as long as the current is on. Because this configuration produces light emission similar to that produced using photoluminescence (PL), we refer to it as liquid contact luminescence or LCL. LCL is a quick, inexpensive, and non-destructive way to obtain information about a variety of material parameters including peak emission wavelength, spectral linewidth, and relative internal quantum efficiency. The use of aqueous electrolytes in the initial LCL experiments resulted in bubble generation. Based on a systematic study of non-aqueous solutions, it was discovered that it was possible to perform LCL without bubble generation and to reduce circuit resistance. As a consequence, we have now demonstrated the feasibility of using the, liquid contact luminescence phenomenon as the basis for a new type of FPD technology. viii CHAPTER 1