Ultra-small red micro-LEDs (<10 μm) with measurable output power have proved difficult to demonstrate. The smallest state-of-the-art red micro-LEDs (AlInGaP) to have exhibited a decent output power of ∼1.75 mW mm⁻² are 20 μm × 20 μm in dimension. InGaN-based red micro-LED development has primarily been impeded due to the large lattice mismatch between the substrate and the quantum wells along with fabrication challenges such as low damage etching. In this work, we demonstrate 6 μm × 6 μm sized InGaN red micro-LEDs with an on-wafer external quantum efficiency of 0.2% and light output power reaching 2.1 mW mm⁻².

Though GaN HEMTs have primarily been used for power amplification, they are also well suited for receiver applications. In the front-end of receivers, non-linearities, in particular third-order intermodulation products lead to in-band signal distortion. The intermodulation distortion is primarily dominated by transconductance and its derivatives. In this paper, we report on N-polar GaN MIS-HEMTs able to simultaneously achieve high gain (12.7 dB) and excellent linearity performance (OIP3/PDC of 15 dB) for low-power receiver application at 30 GHz. With a two-tone load-pull input-bias sweep, we demonstrate that the linearity of high performance HEMTs is sensitive to bias, and we present our measurement methodology to accommodate this.

In this study, two methods to tune the emission wavelength of micro-LEDs fabricated on tile patterned compliant GaN-on-porous-GaN pseudo-substrates (PSs) are presented. The mechanical flexibility of porous GaN was utilized to relax the strain induced during the growth of light-emitting diode (LED) structures with n- and p-InGaN layers and enhance the indium incorporation via the composition pulling effect. The first approach involved only varying the size of the PS square tiles used for LED structure regrowth, from 20 × 20 μm² to 8 × 8 μm². Higher n-InGaN base layer relaxation with decreasing tile size resulted in a red shift of emission from 525 nm to 561 nm with no change in the growth conditions. The second method involved changing the mole fraction, x, of the n-In_xGa_1−xN base layer of the LED structure from 0.04 to 0.09 by reducing growth temperature, while maintaining the high temperature growth conditions of the multi-quantum well (MQW) and p-InGaN targeting 530 nm emission. The resulting wavelength shift was a remarkable 536–616 nm due to the stronger composition pulling effect, providing a pathway to enable high indium content MQW active regions to be grown at high temperature.

The compliant behavior of high fill-factor 10 × 10 μm² square patterned 60–140 nm thick GaN-on-porous-GaN tiles was demonstrated by utilizing porous GaN as a semi-flexible underlayer. High resolution x-ray diffraction measurements showed a larger a-lattice constant of InGaN layers deposited on these patterned GaN-on-porous GaN pseudo-substrates in comparison to those deposited on co-loaded planar GaN-on-sapphire templates. Additionally, InGaN based light emitting diode (LED) structures deposited on these GaN pseudo-substrates exhibited room temperature electroluminescence at 547 nm compared to 506 nm for the LED structures grown on co-loaded planar GaN on sapphire templates, corresponding to a redshift of around 40 nm. The longer emission wavelength was associated with the higher indium incorporation into the InGaN quantum wells deposited on the compliant GaN pseudo-substrates, owing to a reduced lattice mismatch between the quantum well and the n-InGaN base layers grown on the compliant pseudo-substrates, due to the composition pulling effect.

Fully or partially relaxed micron-sized InGaN patterns with fill factors up to 69% were demonstrated via porosification of the underlying GaN:Si layer. The impact of the porosification etch conditions and the pattern geometry on the degree of InGaN relaxation were studied and monitored via high resolution x-ray diffraction reciprocal space maps. Additionally, a 45 nm redshift in the photoluminescence emission from In _x Ga _{1− x} N/ In _y Ga _{1− y} N multi-quantum wells (MQWs) regrown on bi-axially relaxed InGaN buffer layers was observed when compared to a co-loaded reference sample grown on GaN. The longer emission wavelength was associated with higher indium incorporation into the InGaN layers deposited on the InGaN base layers with a lattice constant larger than GaN, due to the reduced lattice mismatch between MQW and InGaN base layer, also called compositional pulling effect.

The compliant behavior of densely packed 10 × 10 µm² square patterned InGaN layers on top of porous GaN is demonstrated. The elastic relaxation of the InGaN layers is enabled by the low stiffness of the porous GaN under layer. High resolution X-ray diffraction measurements show that upon InGaN re-growths on these InGaN-on-porous GaN pseudo-substrates, not only was the regrown layer partially relaxed, but the degree of relaxation of the InGaN pseudo-substrate layer on top of the porous GaN also showed an increase in the a-lattice constant. Furthermore, methods to improve the surface morphology of the InGaN layers grown by metal-organic chemical vapor deposition (MOCVD) were explored in order to fabricate InGaN pseudo-substrates for future optoelectronic and electronic devices. The largest a-lattice constant demonstrated in this study using this improved method was 3.209 Å, corresponding to a fully relaxed InGaN film with an indium composition of 0.056.