HgCdTe molecular beam epitaxy material for microcavity light emitters: Application to gas detection in the 2–6 µm range

Most pollution gases, CO, CO2, NOx, SO2, CH4 …, have fundamental optical absorption in the near infrared range. We report here on microcavity light sources emitting at room temperature between 2 and 6 µm integrated in a gas detection system. HgCdTe has been chosen for this application, among several semiconductor materials. Molecular beam epitaxy (MBE) is very well adapted to grow the suitable HgCdTe heterostructure. The quality of involved HgCdTe layers has to be optimized in order to have a good photoluminescence response at 300 K. For this study, we used the knowledge we acquired in the field of MBE HgCdTe growth for infrared focal plane arrays (IRFPAs). Especially, we took advantage of the substrate preparation before growing and the flux control. We show subsequently several characterization results concerning our material quality. The compact emitting system is formed by this microcavity structure coupled to a 0.8-µm external pumping source. The Fabry-Perot type microcavity is obtained by using two evaporated YF3/ZnS dielectric multilayered Bragg mirrors. We developed several devices exhibiting emission wavelengths at 3.3 µm, 4.26 µm, and 4.7 µm for CH4, CO2, and CO gas measurements, respectively, and 3.7 µm for the reference beam. We measured less than 200 ppm CH4 in a 1 bar mixed gas along a 10-cm-long cell.