Nano-dimensional CdSxSe1-x Millimeter Wave Response Data at Various Laser Fluences

Published: 12-04-2020| Version 1 | DOI: 10.17632/3n9x22rgnv.1
Contributors:
Biswadev Roy,
Marvin Wu

Description

Ternary chalcogenide semiconductor crystalline alloy CdSxSe1-x nanostructures belong to the II-VI group and bear the Wurtzite structure. These nanowires exhibit photoresponsivity and as such, we collected the time-resolved millimeter wave conductivity (TR-mmWC) differential absorption transients for this solid solution nanostructure with x between 0.6 and 0.8 at the center point of the mixture. Transmitted radiofrequency responses are collected as voltage signals from a zero-bias diode (Schottky) detector. The spot of pump and probe beam overlap at a point almost center of the sulfide rich (orange) – selenide rich (red) mixture. The continuous wave probe signal was generated between 110-170 GHz at a beam power level 0.32 mW and an ultrafast 532 nm laser with a width of 0.69 ns was used for the purpose of supplying pump energy at a repetitive frequency of 1000 Hz. The averaged transients attached here are time-voltage datasets for laser power density (PD) between 0.26 and 10.6 micro-Joules per square cm. CdSxSe1-x nanostructures were synthesized via the vapor-liquid-solid mechanism in a hot-wall, tube furnace based system. A 1:1 mixture of CdS and CdSe powders (Alfa Aesar) was loaded into a quartz boat and silicon wafers with 20 nm Au nanoparticles (Ted Pella) deposited by drop coating were placed at the downstream edge of the tube furnace hot zone. The furnace was initially evacuated to a base pressure of 5mTorr, and then flushed repeatedly with Ar gas to remove oxygen. The pressure was set at 200 Torr with an Ar flow rate of 50 standard cubic-centimeter per minute (SCCM) for nanostructure growth, and the temperature was ramped up to 7500 C in 10 minutes. The quartz boat containing the CdS:CdSe mixture was inserted into the center of the furnace hot zone using a magnetically coupled rod after the system reached the growth temperature, and the temperature was maintained for 30 minutes. The boat was then removed from the hot zone of the furnace, and the system was allowed to cool naturally to room temperature overnight. Frequency spectrum of the peak voltage to DC voltage through sample ratio shows an increasing trend at 150 GHz. We note a 0.2% change in TR-mmWC response ratio at 150 GHz with laser power density ~10.6 microJ per sq. cm. A total of 30 .csv data files have been uploaded. These are ASCII delimited data files having two columns column 1: time, and column 2: voltage response from the RF detector after amplification by low noise amplifier with gain 35.7. The probe frequency and laser PD are mentioned in the filenames itself. The usual way to convert 1.3ND (neutral density filter size) laser PD to actual PD in micro-Joules per square cm. would be to use 10.6/10**(1.3); 10.6 microJoules per square cm is the maximum power density for the laser when there is no neutral density filter on path and it is measured using a laser power meter when the repetition rate is 1000Hz. All files pertain to 30% power 0.32 mW.

Files

Steps to reproduce

Grow CdSxSe1-x nanowires with one side Selenide rich and another side Sulfide rich. Illuminate the central mix part with 10.6 microJ per sq. cm laser pulse and pass millimeter wave through the laser spot with ZBD detector to collect the differential absorption signal. Average the signal at least 100 times and store as transient file containing pump-probe delay and corresponding voltages.