What is self selecting vapour growth (SSVG)? 1 Ken Durose and 2Andrzej Szczerbakow 1Department 2Institute of Physics, Univ of Durham, South Road, Durham DH1 3LE, UK of Physics, Polish Academy of Sciences, 32/46 Al. Lotknikow, Warszaw, Poland Piper - Polich Self Selecting Vapour Growth - SSVG ‘Self Selecting Vapour Growth’ is a method of bulk growth in a sealed capsule that is physically distinct from the more well known methods of Piper-Polich and MarkovDavydov growth. Szczerbakow has developed SSVG very extensively, both to understand the driving forces for growth and in the preparation of II-VI and IV-VI single crystals. The method deserves to be more widely appreciated. Self Selecting Vapour Growth offers the following: ¾Growth free from the walls ¾A growth front at the coolest part of the crystal, not the hottest as in conventional methods ¾The growth is therefore not self-limiting ¾Growth is almost isothermal ¾Solid solution crystals grow without distillation-like separation – exceptional compositional homogeneity is possible radiation conduction Markov - Davydov ¾Transport to hottest end of cool seed ¾Transport to hottest end of cool growth tip ¾Seeded growth ¾Unseeded growth ¾Little contact with walls ¾Contact with walls ¾Excess elements condense out at A ¾Poor structural quality ¾Good structural quality C Horizontal SSVG S C (a) (b) Tfront > Tinterior Vertical SSVG S C T front < Tinterior ¾Transport to coolest end of cool seed ¾As for Horizontal SSVG plus… ¾Self – selecting seed Horizontal SSVG M ¾No contact with walls ¾Good structural quality ¾Better control of boule shapes ¾Good compositional uniformity ¾Continuous re-cycling of source and seed Vertical SSVG Offers potential ¾For scale-up ¾Crystal self-refinement 1 – main heater ensuring the plateau near the growth temperature; Pb0.94Sn0.06Se 2 – heater generating the process-driving temperature difference; 3 – heater protecting against condensation in the ampoule top; ¾Growth is in a very small temperature gradient 4 – capillary for condensing traces of an excess element; ¾Source material evaporates from the hot wall 5 – crystal; 6 – thermal insulation. The arrows indicate the main currents of thermal radiation ¾Condensation occurs at the coolest part of the source mass Crystals grown by SSVG PbS PbSe PbTe SnTe CdS CdTe Pb0.8Sn0.2Te CdTe1-xSx (x=0.04) CdTe Cd0.8Zn0.2Te ZnTe Exceptional compositional uniformity of solid solutions PbSe ZnTe Conclusions Solid solution x Variation in x from XRD Variation in x from PL 6000 Cd1-xZnxTe ~0.04 0.001 0.0014 5000 Cd1-xZnxTe 0.2 0.0016 0.0019 4000 CdTe1-xSex 0.05 0.0024 0.0034 3000 CdTe1-xSx ~0.05 0.0013 0.0015 2000 • SSVG is different from other vapour growth methods •Growth is free from the walls, self nucleating, and not selflimiting •Exceptional compositional homogeneity has been demonstrated •Horizontal SSVG works well for small ternary crystals 1000 ¾PL and lattice parameter used to check uniformity ¾Exceptional compositional uniformity over a slice ¾Works well even when binaries have disparate vapour pressures e.g. CdTe - CdS PbSe0.92S0.08 Pb1-xSnxTe 0<x <1 PbSe1-xSex 0<x <1 Pb1-xSnxSe 0<x <0.4 Pb1-xGexTe 0<x <1 (PbSe)1-x(SnTe)x x = 0.1 Cd1-xZnxTe x = 0.04 Cd1-xZnxTe x = 0.2 CdTe1-xSx x = 0.04 CdTe1-xSex x = 0.04 0 1.48 1.50 1.52 1.54 1.56 1.58 •Vertical SSVG will be best for •Scaling up the process •Taking advantage of continuous recycling of the source/crystal to give structural and compositional refinement •Growing boules with controllable shapes Andrzej Szczerbakow and Ken Durose “Self-Selecting Vapour Growth of bulk crystals – principles and applicability” submitted to Progress in Cryst. Growth and Characterisation of Materials