IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Wednesday Sessions
       Session SC+SS+EL-WeA

Paper SC+SS+EL-WeA7
The Study of InP(100) Chemical Cleaning by Synchrotron Radiation Photoemission Spectroscopy

Wednesday, October 31, 2001, 4:00 pm, Room 111

Session: Chemistry of Semiconductor Etching & Cleaning
Presenter: Y Sun, Stanford University
Authors: Y Sun, Stanford University
F. Machuca, Stanford University
Z. Liu, Stanford University
P. Pianetta, Stanford Synchrotron Radiation Lab
W.E. Spicer, Stanford University
Correspondent: Click to Email
The activation process for GaAs negative electron affinity (NEA) photoemitters has been studied extensively. However, the surface chemistry of other NEA materials such as InP is sufficiently different from that of GaAs that additional study is warranted on all aspects of the process starting from the initial surface cleaning to the final activation step. This work will concentrate on the preactivation clean in which the the surface species will be quantified using photoelectron spectroscopy. The goal of this work is to develop clean starting surface that will be used in subsequent activation studies. The cleaning process has three steps, the first two taking place in an argon purged glove bag attached to the load lock of the vacuum system to eliminate atmospheric contamination. Synchrotron radiation is used for the photoemission in order to obtain the necessary surface sensitivity and resolution for the In 4d, P 2p, C 1s and O 1s core levels as well as the valence band. In our most effective cleaning process, the InP is first etched in 4:1:100 H@sub 2@SO@sub 4@:H@sub 2@O@sub 2@:H@sub 2@O and results in a surface with 0.5-1 monolayers of In and P oxides and 0.5-1 ML of C contamination. Note that this is in contrast with GaAs in which this same etching step leaves elemental As and Ga suboxide and thus only requires a subsequent heat treatment to achieve a clean surface. For InP, a second oxide etching step is therefore required. This can either use a 9% HCl or a 1:1 H@sub 2@SO@sub 4@:H@sub 2@O solution both of which result in a hydrophobic surface with 0.3 ML of elemental P, 0.1 ML of C and complete removal of both the P and In oxides,. The lack of any significant amounts of S or Cl on the surface leads us to postulate that this surface is P terminated. Finally, a 360°C anneal in UHV gives a stoichiometric InP surface with no elemental P and only 0.05 ML C. These surfaces are now suitable for similar detailed studies of the full NEA activation process.