Epitaxial Lift-Off of Flexible GaN-Based HEMT Arrays with Performances Optimization by the Piezotronic Effect

Flexible GaN-based ultraviolet microdisk lasers on PET substrate

Flexible optoelectronics is a technique for fabricating optoelectronic devices on a flexible substrate. Compared with conventional devices, flexible optoelectronic devices can be used in more complex working environments benefiting from the mechanical flexibility. Herein, for the first time to the best of our knowledge, a flexible GaN-based microdisk laser on a polyethylene terephthalate (PET) substrate in the ultraviolet A (UVA) range was demonstrated by using thin film transfer process based on laser lift-off (LLO). The lasing wavelength is 370.5 nm with a linewidth of 0.15 nm and a threshold power density of 200 kW/cm². Additionally, a distributed Bragg reflector (DBR) was deposited on the backside of the microdisk as the bottom mirror between GaN microdisk and PET substrate, which can provide better mode confinement inside the microdisk and increases the oscillation intensity. The lasing wavelength of the flexible laser shows a 2-nm redshift under different bending curvature of the substrate, which is promising for applications such as mechanical sensing.

GaN/Gr (2D)/Si (3D) Combined High-Performance Hot Electron Transistors

To overcome the problem of minority carrier storage time in bipolar transistors, a hot electron transistor (HET) has been proposed. This device has the advantage of high working speed and some complex logic functions can be completed by using one component. Here, we demonstrate a mixed-dimensional HET composed of GaN/AlN microwires, graphene (Gr), and Si. The electrons between GaN/AlN are injected into graphene by an F-N tunneling mechanism to achieve high speed hot electrons, then cross graphene by ballistic transport, and are collected in a nearly lossless manner through a low-barrier Si. Therefore, the device shows a record DC gain of 16.2, a collection efficiency close to the limit of 99.9% based on the graphene hot electron transistor (GHET), an emitter current density of about 68.7 A/cm², and a high on/off current ratio reaching ∼10⁷. Meanwhile, the current saturation range is wide, beyond those of most GHETs. It has potential applications as a power amplifier.