Red LEDs were grown by metalorganic chemical vapor deposition with a high active region temperature of 870 °C on a relaxed InGaN/GaN superlattice buffer. The buffer was 100% biaxially relaxed by the thermal decomposition of an InGaN underlayer, measured by high resolution X-ray diffraction. Fabricated LEDs showed a low forward voltage of 2.25 V at a current density of 25 Acm −2 with no Al-containing layers in the active region, a peak emission wavelength of 633 nm at 200 Acm −2 and an on-wafer peak external quantum efficiency of 0.05%. Uniform red emission and relaxation were observed across a two inch substrate.

Compared to graphene and MoS 2 , studies on metal contacts to black phosphorus (BP) transistors are still immature. In this work, we present the experimental analysis of titanium contacts on BP based upon the theory of thermionic emssion. The Schottky barrier height (SBH) is extracted by thermionic emission methods to analyze the properties of Ti-BP contact. To examine the results, the band gap of BP is extracted followed by theoretical band alignment by Schottky-Mott rule. However, an underestimated SBH is found due to the hysteresis in electrical results. Hence, a modified SBH extraction for contact resistance that avoids the effects of hysteresis is proposed and demonstrated, showing a more accurate SBH that agrees well with theoretical value and results of transmission electron microscopy and energydispersive x-ray spectroscopy.

In this work, we demonstrate for the first time an ultra-low contact resistance few-layered black phosphorus (BP) transistor with metallic PGex contacts formed by rapid thermal annealing (RTA). The on-state current of the transistor can be significantly improved and the ION/IOFF ratio increases by almost 2 order. The hole mobility is enhanced by 25 times to 227 cm2V−1s−1. The contact resistance extracted by the transfer length method is 0.365 kΩ∙μm, which is the lowest value in black phosphorus transistors without degradation of ION/IOFF ratio. In addition, the I-V curve of the transistor with PGex contact is linear compared to that with Ti contact at 80 K, indicating that a metallic ohmic contact is successfully formed. Finally, X-ray photoelectron spectroscopy is used to characterize the PGex compound. A signal of P-Ge bond is first observed, further verifying the doping of Ge into BP and the formation of the PGex alloy.

An ohmic contact of graphene/MoS2 heterostructure is determined by using ultraviolet photoelectron spectroscopy (UPS). Since graphene shows a great potential to replace metal contact, a direct comparison of Cr/Au contact and graphene contact on the MoS2 thin film transistor (TFT) is made. Different from metal contacts, the work function of graphene can be modulated. As a result, the subthreshold swing can be improved. And when Vg<VFB, the intrinsic graphene changes into p-type, so graphene contact can achieve lower off current by lowering the Fermi level. To further improve the performance of MoS2 TFT, a new method using graphene contact first and MoS2 layer last process that can avoid PMMA residue and high processing temperature is applied. MoS2 TFT using this method shows on/off current ratio up to 6×106 order of magnitude, high mobility of 116 cm2/V-sec, and subthreshold swing of only 0.515 V/dec.

Electrically driven c-plane InGaN-based blue edge emitting laser diodes on a strain-relaxed template (SRT) are successfully demonstrated. The relaxation degree of the InGaN buffer was 26.6%, and the root mean square (RMS) roughness of the surface morphology was 0.65 nm. The laser diodes (LDs) on the SRT laser at 459 nm had a threshold current density of 52 kA/cm2 under the room temperature pulsed operation. The internal loss of the LDs on the SRT was 30–35 cm−1. Regardless of the high threshold current density, this is the first demonstrated laser diode using the strain-relaxed method on c-plane GaN.