The research of CdZnTe (111)B surface with synchrotron radiation photoemission spectroscopy
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Wenhua Zhang and Faqiang Xu National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China (Received 2 October 2008; accepted 9 December 2008)
The clean and ordered surfaces of CdZnTe (111)B grown by the Bridgman method were obtained by Ar ion bombardment and thermal annealing in situ in an ultrahigh vacuum. The surface atomic structures of CdZnTe (111)B after annealing at different temperature were observed by low-energy electron diffraction (LEED). The valence band and work function of CdZnTe (111)B surfaces were determined by synchrotron radiation photoemission spectroscopy. The order of CdZnTe (111)B after annealing at 350 C will worsen, and the (111)B-(2 2) local reconstruction will be formed. The work function of CdZnTe (111)B after annealing at 350 C is 0.8 eV higher than that of CdZnTe (111)B-(1 1), and the local reconstruction may be induced by Te adatoms on top of the ideal truncation.
I. INTRODUCTION
II. EXPERIMENTAL PROCEDURES
In recent years, there has been increasing interest in the II-VI compound semiconductor CdZnTe for its excellent photoelectric properties, especially for the application of room temperature x-ray and gamma-ray spectrometers due to their wide band gap and high absorption coefficients.1 The surface atomic and electronic structure is a critical factor in determining the properties of the detectors.2 The correlation between atomic and electronic is generally so strong that a realistic description of the surface electronic structure cannot be obtained without the knowledge of the correct atomic geometry. Despite significant progress in studying the surface of CdTe grown by molecular beam epitaxy,3–5 the nature of CdZnTe surfaces remains unknown. In particular, little is known about the surface atomic geometry and electronics of the Te faces of CdZnTe. In our recent research, the surface atomic structure, the surface valence band, and the work function of CdZnTe (111)B surface were studied using low-energy electron diffraction (LEED) and synchrotron radiation photoemission spectroscopy (SRPES).
Cd0.96Zn0.04Te (111) wafers were cut from the undoped CdZnTe ingot grown by a vertical Brigdman method. Crystallographic polarities of (111)B surfaces were identified according to the etched dislocation patterns6 by using the etching solution HNO3 (10 mL), H2O (20 mL), and K2Cr2O7 (4 g). The CdZnTe (111)B surfaces were pretreated with mechanical polishing and etching in 2% (v/v) Br-MeOH solution and then rinsed in deionized water. The chemomechanical polishing was used as the final polishing step after etching to remove the Te enrichment deposited on the surface introduced by etching with Br-MeOH. To dislodge oxygen and other impurity atoms adsorbed on the surface, the sample was etched for 30 min by Ar ion with different ionization voltages (1.5, 1.2, and 1.0 kV). After Ar ion etching, there was no C and O spectra in the x-ray photoelectron XPS full spectra, which suggested that the clean surface was obtained. Subsequently, the sample was
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