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 ingots >50-mm diameter. Physical vapor transport and chemical vapor transport methods have been explored but cannot lead to large ingot/wafer growth of >50-mm diameter. Melt growth techniques have been explored but a phase transition from wurtzite to zincblende occurs at 1425°C, approximately 100°C below the melting temperature of ZnSe. In stoichiometric melt growth, this phase transition leads to twinning problems along the {111} planes disrupting single crystallinity and making mining of (100) wafers not possible. Here, ZnSe will be grown from an off-stoichiometric melt (i.e. melt-solution) using the Accelerated Crucible Rotation Technique (ACRT) combined with high-pressure Bridgman. By using a slight excess of Se in the growth mixture, the melting temperature can be reduced to approximately 1400°C where the phase transition will be avoided and ZnSe will be crystallized in the zincblende phase, thus leading to improved single crystallinity compared to typical melt-growth techniques. This is a process that is similar to the Traveler Heater Method (THM), however without extremely slow growth rates, on the order of 1-mm/day. With an ACRT process, RDT has recently been able to improve stable growth rates, on the order of 1 – 2 mm/hr, for the growth of CdTe and CZT. Additionally, ACRT-produced CdTe and CZT do not require post-growth processing (annealing) to remove (or reduce the size of) the large Te principates that are inherent to THM-grown CdTe and CZT and thus disrupt the electrical and charge collection properties of resulting CdTe and CZT devices. A similar ACRT process will be developed in this effort for the commercial production of (100) ZnSe wafers. RDT has partnered with Dr. Peter Rudolph, a pioneer in II-VI material crystal growth and design. Dr. Rudolph originally grew ZnSe from melt during his time in Japan in the 1990s. Dr. Rudolph will consult RDT in the melt-solution growth of ZnSe here, a process that has not been developed to date. RDT has also partnered with Dr. Santosh Swain of Washington State University, an expert in II-VI crystal growth and numerical modeling. Dr. Swain will lead CGSim (STR, Inc.) numerical modeling efforts to help guide the melt-solution growth developments in high-pressure Bridgman/ACRT ZnSe growth. RDT has a high-pressure Bridgman furnace equipped with ACRT that is currently used to produce group-V doped CdTe for the thin-film photovoltaic industry. RDT has the necessary dicing and polishing equipment needed for the proposed effort. Two ZnSe growth trials will be performed. Samples will be processed from these ingots and characterized for orientation and degree of miscut. A final deliverable 10-mm x 10-mm x 1-mm (100) oriented ZnSe will be delivered by the conclusion of the 6-month Phase I effort.