ZnSe Material Production and Single Crystal Growth by Melt-Solution Using the High-Pressure Bridgman Method

ZnSe is a prime candidate for infrared countermeasure applications having a wider band gap and a wide transparency compared to materials like GaAs. Unfortunately, ZnSe is difficult to grow into large single crystal ingots. Physical vapor transport and chemical vapor transport methods have been explored but cannot lead to large ingot/wafer growth. Melt growth techniques have been explored but a phase transition from wurtzite to zincblende occurs approximately 100°C below the melting temperature of ZnSe leading to twinning problems along the {111} planes and mining of (100) wafers not possible. Here, ZnSe was grown from an off-stoichiometric melt (i.e. melt-solution) using the Accelerated Crucible Rotation Technique (ACRT) combined with high-pressure Bridgman (ACRT-HPB). Using a slight excess of Se in the growth mixture, the melting temperature can be reduced to <1400°C where the phase transition will be avoided and ZnSe will be crystallized in the zincblende phase. RDT modified a high-pressure Bridgman furnace equipped with ACRT in Phase I efforts to perform single crystal growth of ZnSe. Growth trials were performed in phase I using an off-stoichiometric melt having 15% excess Se. The second growth resulted in a high degree of single crystallinity with secondary phases in the bulk. Radial wafers were cut, and samples were polished to a reasonable optical quality. Xray measurements confirmed a main orientation of (111) for radial wafers. Oriented cuts, 54.7° from the (111) and into the (100) were made and 10mm x 10mm x ~1mm thick (100) oriented ZnSe sample were demonstrated. There are four major objectives in Phase II to further develop a robust ACRT-HPB process to grow single crystal ZnSe ingots. (1) Modifications will be made to the existing ACRT-HPB furnace to help stabilize the ACRT rotation and profile and help stabilize the thermal profile. These improvements will promote the Se at the growth interface to redistribute into the Se-rich layer and reduce Se precipitation in the ZnSe bulk, thus producing an ingot of increased single crystallinity and transparency. An advanced ACRT-HPB will be built out capable of growing 75-mm diameter ingots, where 50mm x 50mm oriented wafers can be harvested. This furnace will be designed for improved thermal control by having three controlled heater zones. (2) A series of six ZnSe growths will be performed where each growth process will be iterated, applying lessons learned from each process. (3) The ingots produced in Phase II will be processed to harvest (100) oriented wafers from the ingot. (4) The orientated wafers will be lapped and polished to achieve a surface finish quality of 40 – 20 scratch-dig in year 1 and will be further developed to achieve a scratch dig of 20 – 10 in year 2. Industrial lapping/polishing tools secured and brought online will introduce automation and increase repeatably to the polishing process. Several samples having dimensions between 25mm x 25 to 50mm x 50mm will be delivered.