Growth and Characterization of CDTE and CDTE Alloys
- PDF / 1,869,164 Bytes
- 12 Pages / 420.48 x 639 pts Page_size
- 48 Downloads / 188 Views
GROWTH AND CHARACTERIZATION OF CDTE AND CDTE ALLOYS S. MCDEVITT*, D.R. JOHN*, J.L. SEPICH*, K.A. BOWERS**, J.F. SCHETZINA**, R.S. RAI***, AND S. MAHAJAN*** *II-VI Incorporated, 375 Saxonburg Boulevard, Saxonburg, 16056 **North Carolina State University, Department of Physics, Raleigh, NC 27695 ***Carnegie Mellon University, Department of Metallurgical Engineering and Materials Science, Pittsburgh, PA 15023
PA
ABSTRACT Methods used to grow bulk, CdTe crystals, effects of alloying on their perfection and typical single crystal properties are reviewed in this paper. Crystals grown by a modified horizontal Bridgman technique have lower dislocation densities than those grown by a modified vertical Bridgman method. Dislocation densities of the order of ~lx103/cm2 have been observed in CdTeSe crystals grown by the former technique. Due to the difference in the distribution coefficients of Zn and Se in CdTe, CdTeSe ingots are chemically more uniform than CdZnTe ingots. Purity studies of starting materials indicate that Se substitutions may introduce more impurities than Zn additions. INTRODUCTION CdTe and CdTe alloys are used as substrates to grow HgCdTe, HgZnTe and HgMnTe epitaxial layers. These epitaxial materials are being developed for infrared detection and optoelectronic applications. Although HgCdTe can be grown by bulk crystal growth methods [1,2], the demand for large-area infrared (IR) devices has increased dependence on epitaxial HgCdTe to produce large scale, detector grade material. A variety of epitaxial growth techniques, such as liquid phase epitaxy (LPE), organo-metallic vapor phase epitaxy (OMVPE), and molecular beam epitaxy (MBE), have been used to deposit epitaxial layers. In addition, since the perfection of CdTe substrates is not very high, alternative substrates, InSb, GaAs, and Si, have been used. However, CdTe and CdTe alloys have the advantage of chemical compatibility and closer lattice match. BULK CRYSTAL GROWTH It is well documented that the performance of heterostructure devices is strongly influenced by the quality of the underlying substrate [3]. Dislocations present in the substrates are observed to be replicated into epitaxial layers grown by MBE [4], OMVPE [5], and LPE [6]. Therefore in addition to growing large area single crystals, a bulk crystal growth method should be optimized to produce material with low dislocation density, high IR transmission, high resistivity, and absence of second phase particles. Vertical Bridgman with and Horizontal Bridgman with OverPressure OverPressure (VBOP) (HBOP) have the advantages of producing large area, high quality, and stoichiometric crystals as compared to the three other growth Mat. Res. Soc. Symp. Proc. Vol. 161. ©1990 Materials Research Society
16
techniques - heat exchanger method (HEM), traveling heater method (THM) and high pressure Bridgman. THM offers the advantage of lower processing temperatures to produce a "purer" material. This method has been used advantageously in the growth of Cdl-xMnxTe, where x > 0.15, to avoid a high tempe
Data Loading...
