Available Technology

A Method for Producing Compound Semiconductors

Improving Yield with a New Physical Vapor Transport Process
Vapor growth techniques have significant advantages over melt growth, resulting from (1) lower processing temperatures, (2) purification processes associated with vapor growth, and (3) improved structural quality of grown crystals. However, the main disadvantages associated with this technique have been the waste of untransported starting materials, and low, inconsistent crystal growth rates that reduce yield. The process for growth of semiconductors from vapor has been done traditionally in a quartz ampoule that is vacuum sealed. Diffusion from external atmosphere at processing temperatures (above 1000&#176C), however, results in a loss of vacuum and contamination that is detrimental to crystal growth rate. NASA MSFC&#39s Method for Producing Compound Semiconductors provides a solution to the difficulties mentioned above. The new process involves enclosing the first growth ampoule in a second vacuum ampoule, which preserves the low pressure and mitigates contamination in the growth chamber. Using this process, a growth yield of over 98% was observed for a ZnSe semiconductor crystal, while the growth rate doubled from 5 mm/day to 10 mm/day. The new process is applicable to the vapor growth of group II-VI semiconductors (ZnTe, CdS, ZnSe, ZnS, ZnSeTe, and ZnSeS) as well as group IV-VI semiconductors (PbTe, PbS, PbSe, and PbTeSe).
Abstract: 
Innovators at the Marshall Space Flight Center (MSFC) have developed a novel process for producing compound semiconductors using vapor growth techniques. This innovation implements a unique physical vapor transport (PVT) setup with an extra outer layer of evacuated closed tube to reduce the external vapor pressure diffusing into the growth ampoule. The new process greatly improves the production yield and growth rate, allowing for routine production of high-quality single crystals of compound semiconductors.
Benefits: 

Improved yield and growth rate: By conducting a simple additional step in the preparation of ampoules for semiconductor crystal growth, it is possible to improve yield and growth rate by as much as 100%.

applications: 

Optical devices using wide band gap semiconducting materials

Lasers in the visible spectrum

Infrared Lasers

Optical displays

Digital optical computers

High density recording

Military communications

Reps: 
Patent Number: 
Internal Laboratory Ref #: 
MFS-TOPS-92
Patent Status: 
Patent Issue Date: 
November 27, 2018
Agency
NASA
Region
Southeast
State: 
Alabama
Phone: 
256-544-9151
Email: 
terry.taylor@nasa.gov
Lab Representatives
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