CETUS Group, University of Delaware

Microdisk Report Wednesday, February 02, 2000

To fabricate THz microdisk resonators, we used bulk SiGe layers grown on a p-doped buffer layer to enable selective etching. Using chemical vapor deposition (CVD) in the group of D. Bensahel at CNET in Grenoble, France. The Ge content in the alloy was 5 atomic %. The CVD system was an ASM Epsilon III reactor. The pedestal layer was B-doped so that a selective etch could be used to create a microdisk. The layers were etched to form the cylindrical disks as shown in the SEM figure below. The etching steps are being optimized to obtain the final structure with sufficient undercutting to produce a microdisk surrounded by air on 3 sides. 

SEM micrograph of SiGe microdisk resonators for THz laser sources. Disks are 25 m m in diameter on Si substrate. Disk thickness is 3 microns, and height of pedestal above Si substrate is 7 microns. Vertical modes were measured using FTIR. For lasing action, gain will use intersubband hole transitions in Si/SiGe quantum wells. Feedback will use azimuthal whispering gallery modes. Optical confinement occurs by the higher dielectric constant of the SiGe upper disk with respect to the Si substrate and the surrounding air.

FTIR reflection spectra for incident light normal to the 20 m m diameter micro-disk. Three different microdisks are shown. The oscillations illustrate vertical mode confinement. The dotted line shows the reflectance spectra of the adjacent substrate, confirming that the oscillations are from the microdisk.

(click on the images to enlarge)

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