Quantum Dots (QDs) with it’s high photoluminescent quantum yield and absorption cross section have been established as a material of choice for color conversion applications. For a long time the industrial use of QDs has been restricted to a remote phosphor approach in liquid-crystal displays due to poor photothermal stability. While a lot of progress has been obtained for Cd-based QDs, the Cd-free alternatives are lagging behind. At QustomDot we have made a lot of progress towards obtaining photostable Cd-free QDs, currently surviving high blue light fluxes of 0,5-1,5 W/cm2. We are presenting an overview of major challenges in developing QDs for microLED applications and main factors impacting the degradation mechanism of QDs under blue light illumination.
Using the differential thermal analysis we investigated parameters of melting and crystallization processes of the CdTe based phase in CdTe-Al system near the CdTe side (CdTe + 2 mol. % Al, CdTe + 4 mol. % Al and CdTe + 6 mol. % Al). Varying temperatures of the melts intermediate isothermal holding for 10-, 30- and 60 minutes during their heating up to 1423 K we determined conditions of the melts full homogenization. It was concluded about change of the CdTe phase melting mechanism with Al content rise.
We explored the influence of Cd(Zn)Te detectors on the detector’s dark current for different methods of
contact formation and passivation of the side surfaces. Our findings suggest that the dark current of a
homogeneous detector with ohmic contacts is limited by the detector’s resistivity and the operating voltage.
Detectors with a rectifying barrier have a markedly lower dark current at the same voltage and contact
geometry than those without such a barrier, and their sides have a larger space charge than those of untreated
ones. The major factor lowering the detector’s dark current is the formation of a rectifying barrier that occurs
while creating contacts to the detector; the role of passivation of the lateral surface in this case is minimal.
However, passivation plays the main role in the formation of leakage current in homogeneous detectors with
ohmic contacts, where the uniformity of the electric field is important inside the detector, or in other studies
used for determining the bulk resistivity of the detector material. We formed a surface-barrier structure on a
semi-insulating Cr-Cd(Zn)Te-Cr crystal (n-type) with a resistivity of 1010 Ohm-cm at room temperature. The
measured leakage current of this detector was less than 3 nA at 1500 V. We discuss our findings on this
detector’s structural properties.
We evaluated the effect of high-temperature treatment of Cd0.9Zn0.1Te:In single crystals using Hall-effect measurements,
medium- and high-temperature annealing under various deviations from stoichiometry, and infra-red (IR) transmission
microscopy Annealing at ~730 K sharply increased the electrical conductivity (by ~1-2 orders-of-magnitude). Plots of
the temperature- and cadmium-pressure dependences of the electrical conductivity, carrier concentration, and mobility
were obtained. Treating previously annealed Cd-samples under a Te overpressure at 1070 K allowed us to restore their
resistance to its initial high values. The main difference in comparing this material with CdTe was its lowered electron
density. We explained our results within the framework of Kröger’s theory of quasi-chemical reactions between point
defects in solids.
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