IV–VI Semiconductor growth on silicon substrates and new mid-infrared laser fabrication methods

This paper reviews results from research conducted at the University of Oklahoma on the development of new IV–VI semiconductor (lead salt) epitaxial growth and laser fabrication procedures that can ultimately lead to dramatic increases in mid-IR laser operating temperatures. Work has focused on growth of IV–VI semiconductor laser structures on silicon substrates using buffer layers that contain BaF2. Recent experiments show that it is possible to obtain high crystalline quality IV–VI semiconductor layer structures on (111)-oriented silicon substrates using molecular beam epitaxy (MBE) or on (100)-oriented silicon using a combination of MBE and liquid phase epitaxy (LPE). Experimental data for IV–VI semiconductor layer structures grown on silicon substrates including crystalline quality information as determined by high resolution X-ray diffraction (HRXRD) measurements and absorption edge information as determined by Fourier transform infrared (FTIR) transmission measurements are presented. Results show that these materials can be used to fabricate lasers that cover the 3 μm (3333 cm−1) to 16 μm (625 cm−1) spectral range. Removal of IV–VI semiconductor laser structures from the silicon growth substrate by dissolving BaF2 buffer layers with water is also demonstrated. This allows epitaxially-grown laser structures to be sandwiched between two heat sinks with a minimum of thermally resistive IV–VI semiconductor material. Theoretical modeling predicts that IV–VI lasers fabricated this way will have maximum continuous wave (cw) operating temperatures at least 60° higher than those of IV–VI lasers fabricated on PbSe or PbTe substrates.