150 GHz photoconductivity response of the multilayered structure with alternating SiO2 (2nm) and Ge (4nm) annealed at various temperatures

Published: 14-04-2021| Version 2 | DOI: 10.17632/94k52dg4hg.2
Biswadev Roy,
Branko Pivac,
Marvin Wu


Semiconductor nanoparticles such as Germanium nanocrystals (Ge-nc) embedded in silicon dioxide (SiO2) are becoming a popular MOS candidate for high-speed and low-power-consuming memory devices. Strong charge retention (memory effects) is exhibited when Ge-nc is embedded in silicon dioxide layers (on Si substrate). At nanometer thicknesses, material properties are determined from quantum confinement. Multilayer structure consisting of alternating layers of SiO2 and Ge-nc were produced (one with no annealing and 6 with 1-hour duration annealing done 500° C and 700° C at increments of 25 °C under a dry flow of pure nitrogen). Stacked continuous amorphous SiO2/Ge-nc layers were deposited using the electron gun-assisted physical vapor deposition (PVD) technique. SiO2 layers are used as spacer layers (2nm). All 7 samples are used for obtaining free-space contactless time-resolved millimeter-wave conductance (TR-mmWC) responses at a fixed probe frequency of 150 GHz using variable pump fluences were fixed at 10.1 (data label as FullLaserPower), 2.7 (data labeled as 0.6 ND), and 1.5 (data labeled as 0.6ND) microJoules per square cm from a 532nm ultrashort pulse laser system (one data point at each fluence level for each sample). ND stands as an abbreviation for the neutral density filter size used during the data collection. We collected data that reflect changes in photo-emission induced transmission & reflection radiofrequency voltages and dark (no laser stimulus) dc responses of SiO2/Ge-nc transmitted through the sample as a function of laser fluence. Preliminarily, we find that the peak voltages in the RF transients increase with laser fluence for the sample that was annealed in a nitrogen environment at 700 deg. C. There is a general trend of increase of the rise time with annealing temperature when the laser is fired into the sample and, the same sample shows an appreciable growth of the Shockley-Read-Hall (SRH) decay constant changing from very small to about 7.5 microseconds when the laser fluences are 10 microJoules/cm2. These files are also ASCII-delimited comma-separated variable (.csv) files obtained after low noise amplification with gain ~34.5 and averaging about 5000 times. The free space DC voltages obtained for each sample run are 394 mV for all samples (sample-1 through sample 7) respectively. The DC voltages measured through each sample during the experiments were 244, 277, 163, 242, 267, 255, and 275 mV respectively. Column 1 represents the delay (seconds) and column 2 is the RF voltage (Volts) after amplification. The filename themselves provide the sample number (sample 1 is no annealing performed, Sample-2 annealed at 500 deg C, sample-3 annealed at 525 deg C, sample 4 annealed at 550 deg C, sample 5 annealed at 575 deg C, sample-6 annealed at 600 deg C, and sample-7 annealed at 700 deg C. All transient RF and DC data collected at probe frequency 150 GHz. A flag value 7.8462e+34 should be accounted for in data.


Steps to reproduce

We used TR-mmWC setup (Roy, et al., Rev. Sci. Instrum., Vol. 89, 104704, 2018) to characterize transmission related responses at 150 GHz probe frequency while the silicon dioxide with Germanium nanocrystals wafer is illuminated using an ultrafast 532 nm laser source. Laser fluences are varioed between 0, 0.6 and 0.9 ND (neutral density filter) for a nominal laser power (without filter) at 10.1 micro J per cm square.