On favorable thermal fields for detached Bridgman growth

Abstract

The thermal fields of two Bridgman-like configurations, representative of real systems used in prior experiments for the detached growth of CdTe and Ge crystals, are studied. These detailed heat transfer computations are performed using the CrysMAS code and expand upon our previous analyses [14] that posited a new mechanism involving the thermal field and meniscus position to explain stable conditions for dewetted Bridgman growth. Computational results indicate that heat transfer conditions that led to successful detached growth in both of these systems are in accordance with our prior assertion, namely that the prevention of crystal reattachment to the crucible wall requires the avoidance of any undercooling of the melt meniscus during the growth run. Significantly, relatively simple process modifications that promote favorable thermal conditions for detached growth may overcome detrimental factors associated with meniscus shape and crucible wetting. Thus, these ideas may be important to advance the practice of detached growth for many materials.

Existence, stability, and nonlinear dynamics of detached Bridgman growth states under zero gravity

“…The heat transfer computations showed that stable operating states exist with a narrow gap width but that the temperature field near the meniscus is sensitive to gap thermal conditions. Notably, the melt near the meniscus-ampoule wetting point could become supercooled under certain conditions, consistent with our prior analyses [32,62]. These phenomena certainly merit further study, since undercooling could lead to reattachment of the crystal to the ampoule wall.…”

“…Another effect is a flattening of the crystal-melt interface near the TPL, which causes a transition from a concave interface to a slightly convex one in the vicinity of the TPL. A similar heat transfer situation, with undercooling predicted along the meniscus during detached Bridgman growth, was first noted by Stelian et al [32,62].…”

“…With regard to freeze-off, the possibility of melt undercooling discussed above and in Refs. [32,62] is an additional factor to consider.…”

“…The undercooling effect is a function of both heat transfer and meniscus shape [62], as shown in Fig. 4, which explores the effect of static wetting angle on meniscus shape and local heat transfer for the base case B of Fig.…”

Influence of the dewetting phenomenon on the zinc distribution in CdZnTe crystals grown by dewetted Bridgman technique

“…This material is also extremely difficult to grow and has been the object of numerous studies: notable microgravity experiments by Larson et al. [1][2][3][4] on USML-1/STS-50 and USML-2/STS-73, and by Fiederle, Duffar and co-workers 5,6 on AGHF1/STS-95; experiments in terrestrial conditions [7][8][9][10][11][12][13][14][15] using floating zone, traveling heater method, horizontal Bridgman, high-pressure vertical Bridgman, detached Bridgman techniques; and extensive modeling by Derby et al [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] , Duffar and Sylla 12,33 . Cadmium telluride and its alloys have unusual thermophysical properties which make their growth very different from other semiconductor crystals.…”