OBSERVATION OF DOUBLE HETEROSTRUCTURES FOR LASER-DIODES USING SCANNING TUNNELING MICROSCOPY AND CURRENT IMAGING TUNNELING SPECTROSCOPY IN AIR

The cleaved surfaces of the double heterostructures (η-InP/InGaAsP/ρ-InP) for laser diodes have been directly observed in air using scanning tunneling microscopy (STM) and current imaging tunneling spectroscopy (CITS). CITS measurements enable us to observe each layer of the double heterostructures. Since local current voltage characteristics depend on the tunneling voltage which determines the tip—sample separation, we can obtain different current voltage characteristics for each layer by selecting a proper tunneling voltage. Each layer of the double heterostructure is identified by the difference in the tunneling current. In order to investigate the lateral distribution of Zn at the η-InP/InGaAsP interface, we have used STM measurements and a stain-etching method whose etching rate is sensitive to the existence of ρ-type impurity. STM images of the stain-etched cleaved surfaces show hollows straggled along the η-InP/InGaAsP interface. This result reveals that the impurity pileup is localized along the interface, which can not be observed by secondary ion mass spectroscopy (SIMS) analysis. © 1990, American Vacuum Society. All rights reserved.