Extremely narrow violet photoluminescence line from ultrathin InN single quantum well on step-free GaN surface.

An ultrathin (one monolayer thick) InN single quantum well (SQW) formed on a step-free GaN surface shows very sharp violet PL emission. The size (16 µm in diameter) is large enough for state-of-the-art nanotechnology to handle. Longer wavelength emissions, such as green and red, are expected by increasing the thickness of the SQW through the utilization of the quantum size effect.

Layered boron nitride as a release layer for mechanical transfer of GaN-based devices.

Nitride semiconductors are the materials of choice for a variety of device applications, notably optoelectronics and high-frequency/high-power electronics. One important practical goal is to realize such devices on large, flexible and affordable substrates, on which direct growth of nitride semiconductors of sufficient quality is problematic. Several techniques--such as laser lift-off--have been investigated to enable the transfer of nitride devices from one substrate to another, but existing methods still have some important disadvantages. Here we demonstrate that hexagonal boron nitride (h-BN) can form a release layer that enables the mechanical transfer of gallium nitride (GaN)-based device structures onto foreign substrates. The h-BN layer serves two purposes: it acts as a buffer layer for the growth of high-quality GaN-based semiconductors, and provides a shear plane that makes it straightforward to release the resulting devices. We illustrate the potential versatility of this approach by using h-BN-buffered sapphire substrates to grow an AlGaN/GaN heterostructure with electron mobility of 1,100 cm(2) V(-1) s(-1), an InGaN/GaN multiple-quantum-well structure, and a multiple-quantum-well light-emitting diode. These device structures, ranging in area from five millimetres square to two centimetres square, are then mechanically released from the sapphire substrates and successfully transferred onto other substrates.