Discipline: Technology and Engineering
Subcategory: Materials Science
Candice Forrester - The City College of New York
Co-Author(s): Thor A. Garcia, The City College of New York, New York, NY; Ido Levy, The City College of New York, New York, NY; Kuaile Zhao, The City College of New York, New York, NY; Maria Tamargo, The City College of New York, New York, NY
A novel II-VI/III-V hybrid quantum cascade detector (QCD) was characterized to reveal the unique properties of each layer of the device. The ideal growth conditions for thin-film II-VI and III-V semiconductor materials deposited by molecular beam epitaxy have been explored on InP substrates. The growth parameters used affect the surface morphology and the physical and optical properties of the crystal structures. The quality of a crystal structure is also influenced by its lattice mismatch to the substrate. Characterization techniques such as X-Ray diffraction and photoluminescence spectroscopy (PL) were implemented to analyze the crystal quality and composition. After defining the ideal parameters for test ZnCdSe/InP samples, those conditions were applied to a more complex structure, a hybrid II-VI/III-V quantum cascade detector (QCD). In the calibration series four test samples were evaluated, Samples A, B, C, and D. The results showed Samples C and D had the smallest Full-Width-Half-Maximums (FWHM), 55 meV and 56 meV, respectively indicating good crystal quality. Samples C and D were also the most closely lattice matched, 0.18% and 0.16%, respectively. Using the growth conditions of Samples C and D, a hybrid QCD was created. After growth, the individual epilayers of the hybrid QCD structure were evaluated using depth-resolved PL in which a 1% bromine methanol solution was used to remove layers of material, followed by PL measurements after each etch step. For the PL measurements, the samples were loaded into a cryostat and it was pumped below 10-7 mbar to create a vacuum. The cryostat was then cooled with liquid nitrogen to 77K with the samples positioned at a 45˚ angle with respect to the laser beam. The PL emission spectra of each sample were collected using a Princeton Instruments Acton SP2150 spectrometer with a Princeton Instruments Acton Pixis 256 detector. With this experimental method, the different components of the hybrid II-VI/III-V QCD could be individually measured. The top ZnCdSe surface is known to have a 2.1 eV energy gap. After etching for 3 minutes in the 1%bromine methanol solution, the PL spectrum peaks at 2.25 eV indicating that the MQW core region is exposed. At 8 minutes of etching, on a unique position of the sample, a second peak becomes present; the second peak appears around 2.1 eV. This indicates that the bottom bulk ZnCdSe layer is becoming exposed. At another position of the sample, the MQW peak has almost disappeared, as the bulk ZnCdSe signal is much stronger. After 13 minutes of etching, there is almost no signal in the visible wavelength range, indicating that the full II-VI component of this structure was etched away. The results confirm that the grown structure was consistent with the desired structure.
Funder Acknowledgement(s): This work is supported by the National Science Foundation CREST Center for Interface Design and Engineered Assembly of Low Dimensional systems (IDEALS), NSF grant number HRD-1547830. This research was supported by NIH grant number R25GM056833-16. This work was also supported by the CCAPP-STEP grant at CCNY.
Faculty Advisor: Dr. Maria Tamargo, firstname.lastname@example.org
Role: My role in this research was to verify the growth of the calibration series samples and the II-VI/III-V heterostructure quantum cascade detector. To verify the samples grown, I characterized them using several techniques including photoluminescence spectroscopy to probe the samples' physical properties. In this study, I analyzed the epilayers of the material by using a 1% bromine methanol solution to etch away the individual layers of the material and using a 325 nm He-Cd laser to measure the energy gap of the respective epilayer. Finally, I plotted the data using Origin.