VerLASE Technologies LLC of Bridgewater, NJ, USA (a spin-off from technology development firm Versatilis LLC of Shelburne, VT, USA) says that the US Patent Office has issued US Patent No. 9,269,854, a fundamental patent covering the use of two-dimensional (2D) semiconductor materials as the active, light-emitting layer in LEDs, laser diodes and other optoelectronic devices.
The technology enables low-cost, novel electroluminescent devices, which can be tailored to directly emit in any color in the visible, or in a mixed combination for white light at a desired color temperature, without phosphors or other color-converting media. Such devices can be made entirely of inorganic materials using existing, often depreciated silicon foundries, or even made using liquid chemistry with well accepted, scalable techniques.
VerLASE says that the technology, which can also be hybridized with some organic layers, challenges organic light-emitting diodes (OLEDs) in applications requiring smaller pixel sizes, such as micro-displays for augmented and virtual reality applications, where OLEDs have had extreme difficulty in achieving small pixels with sufficient brightness. Other applications include smaller displays of all kinds, ranging from wearables to smartphone and tablet screens, offering a practical way around some of the technical and cost hurdles pacing broader adoption of OLEDs.
Semiconducting 2D materials like graphene have captured a much attention for their potential use in multiple applications. Such materials can be grown in crystalline layers that are weakly bound to each other (like sheets in a ream of paper) and can be readily cleaved or exfoliated into extremely thin layers. The firm has been investigating using photoluminescent quantum wells (QWs) made from nano-platelets (NPLs) of 2D materials (such as gallium selenide, gallium sulphide and tungsten disulphide) as highly efficient down-converting phosphors that can also be free of cadmium or other heavy metals.
VerLASE had previously secured a broad patent (US 9,035,344) covering the use of such 2D semiconductor materials as phosphors, analogous to quantum dots (QDs) but in a 'flat' or 2D aspect. The new patent extends this work to cover use of such 2D materials as electroluminescent layers in active devices, solidifying the firm's IP portfolio in 2D materials.
QDs were originally envisioned as being disruptive in a similar way for electroluminescent devices, but have so far been used successfully mainly as remote phosphors in LCD displays for modifying backlighting color. They face numerous challenges in expanding their applications range, particularly to active layers, and the best QD materials to date typically contain cadmium.
At the same time, an emerging body of research around the world points to the inherent advantages of 2D semiconductor materials for a wide range of applications. They offer similar optical advantages as QDs with narrow spectral characteristics, better colors and color saturation, but with better efficiency and much better thermal characteristics for superior stability in many lighting, projector and display applications, says VerLASE.
It can also be easier to work with 2D semiconductor materials in depositing the other layers needed to make active devices, the firm adds. VerLASE is in the process of showing simple, working prototypes of such electroluminescent devices, thinning down the active 2D layer to demonstrate direct red, green and blue emission.
"The unique attributes of 2D QWs can enable the original QD vision of inorganic electroluminescent devices," believes chief technical officer Ajay Jain (inventor of the technology), adding that the same basic 2D semiconductor materials can also be used as gain media for lasers and other high-value electro-optical devices.