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Electro-optic (EO) modulators with a high modulation bandwidth are indispensable parts of an optical interconnect system. A key requirement for an energy-efficient EO modulator is the low drive voltage, which can be provided using a standard complementary metal oxide semiconductor circuity without an amplifying driver. Thin-film lithium niobate has emerged as a new promising platform, and shown its capable of achieving driverless and high-speed EO modulators. In this paper, we report a compact high-performance modulator based on the thin-film lithium niobate platform on a silicon substrate. The periodic capacitively loaded travelling-wave electrode is employed to achieve a large modulation bandwidth and a low drive voltage, which can support a driverless single-lane 100Gbaud operation. The folded modulation section design also helps to reduce the device length by almost two thirds. The fabricated device represents a large EO bandwidth of 45GHz with a half-wave voltage of 0.7V. The driverless transmission of a 100Gbaud 4-level pulse amplitude modulation signal is demonstrated with a power consumption of 4.49fj/bit and a bit-error rate below the KP4 forward-error correction threshold of 2.4×10−4.

Multi-lane integrated transmitter chips are key components in future compact optical modules to realize high-speed optical interconnects. Thin-film lithium niobate (TFLN) photonics have emerged as a promising platform for achieving high-performance chip-scale optical systems. Combining a coarse wavelength-division multiplexing (CWDM) devices using fabrication-tolerant angled multimode interferometer structure and high-performance electro-optical modulators, we demonstrate monolithic on-chip four-channel CWDM transmitter on the TFLN platform for the first time. The four-channel CWDM transmitter enables high-speed transmissions of 100 Gb/s data rate per wavelength channel (i.e., an aggregated date rate of 400 Gb/s).

Ultraviolet light-emitting diodes (UVLEDs) with staggered barriers have been studied. The energy band diagrams, internal quantum efficiency, total output power and radiative recombination rate are investigated by APSYS software. The simulation results show that the UVLED with staggered barriers get a little enhancement comparing to the conventional one, on the contrary the structure with p-doped staggered barriers has higher efficiency and power due to enhancement of the holes' injection and the electrons' confinement. Then structures with different Al content in the Mg-doped barriers have been studied numerically and that confirmed the best.

Al x Ga 1-x N/Al 0.6 Ga 0.4 N graded superlattice hole blocking layers (GSL-HBLs) and Al x Ga 1-x N/Al 0.6 Ga 0.4 N graded superlattice electron blocking layers (GSL-EBLs) are applied to the traditional AlGaN-based ultraviolet light-emitting diodes (UVLEDs). This can obtain much higher internal quantum efficiency (IQE) and output power. In order to reveal the underlying physical mechanism of this unique structure, we have studied it numerically by APSYS simulation programs. We find that GSL-EBLs can obviously increase the electron potential height and reduce the hole potential height, produce less electron leakage and more hole injection, leading to higher carrier contration. GSL-HBLs can obviously reduce the hole leakage, reduce the thermal velocity and correspondingly the mean free path of the hot electrons, and increase the electron injection. This enhanced the electron capture efficiency of the multiple quantum wells, which can also help to reduce electron leakage.

The application of a p-type superlattice hole reservoir layer in the traditional ultraviolet light-emitting diodes (UVLED) can obtain better Internal quantum efficiency (IQE) and output power, ease the problem about efficient carrier movement in high Al-content AlGaN material. Through computation and analysis by using the APSYS simulation software, the change of position of the hole reservoir layer can influence the luminous efficiency. The design of a superlattice hole reservoir layer between electron blocking layer (EBL) and p-type AlGaN layer can obviously reduce the hole potential height and increase the electron potential height, produce more hole injection and less electron leak, leading to higher carrier concentration, so as to realize the further increased for carrier recombination rate.

Ultra violet light-emitting diodes (UVLEDs) with different types of Mg-doped barriers have been studied. The energy band diagrams, internal quantum efficiency, total output power and radiative recombination rate are investigated by APSYS software. The simulation results show that the UVLED with only a p-doped top barrier get little enhancement comparing to the conventional one, on the contrary the structure with p-doping in all but the bottom barriers has a much better optical and electrical properties due to enhancement of the holes’ injection and the electrons’ confinement. The efficiency droop is significantly alleviated and the light output power is greatly enhanced. To avoid forming a PN junction by the bottom barrier and the n-AlGaN in the proposed structure, therefore, the bottom barrier isn’t p-doped. Then structures with different hole densities in the Mg-doped barriers have been studied numerically and that confirmed the best.

Optical performances of blue InGaN light-emitting diodes (LEDs) with an undoped AlGaN electron-blocking layer (U-AlGaN EBL) embedded in the active region are investigated numerically. As a benefit of this special structural design, the electrons would spill over the EBL and recombine with the holes in the wells close to the p-side. Moreover, holes in the wells that are close to the n-side increase to a higher concentration due to the presence of a new shallow potential well in the valence band. The simulation results indicate that the LEDs with U-AlGaN EBL has higher internal quantum efficiency as well as light output power compared with the conventional single p-type AlGaN EBL structure. These improvements are primarily contributed to the enhancement on electrons confinement and holes injection.

This paper principally presents the numerical investigation of electron blocking layers (EBL) structures with different Al concentration gradient changing in AlGaN-based deep ultraviolet light emitting diodes (DUV-LEDs). Compared to conventional EBL structure with constant Al composition, the LED with inverted-V-shaped EBL structure has higher output power and carriers recombination rate, but the efficiency droop will decrease obviously while the electron leakage current can reduce much as well. Therefore, the result indicates that appropriate Al component in LED can enhance electron and hole recombination rate in the active region. The improved performance is mainly attribute the sufficient electron-barrier height and relatively higher hole injection efficiency which results from the mitigated band-bending.

InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) with the step stage MQW structure have been investigated numerically. LEDs exhibit enhanced light output power and reduced turn-on voltage with the step stage MQW. Simulated results show that the improvement is mainly due to the modified band bending which is related to the polarization effect. Although the good crystalline quality can reduce the nonradiative recombination, it seems that the impact is small and non-dominant in the performance improvement.

In the present study, spectral tuning of dual-wavelength emission in monolithic InGaN/GaN multiple-quantum well light-emitting diodes was investigated based on an experiment. The reference InGaN/GaN QWs are composed of GaN barriers and “three layers” wells containing a “wetting layer”, a grading layer and a relatively low indium content InGaN layer, which has been grown in the laboratory. The simulation results show that the short wavelength light-emitting peak rises with the increasing of the grading layer thickness. In the meantime, when the thickness of the low indium content InGaN layer decreases, the long wavelength light-emitting peak falls. Dual-wavelength emissions can be achieved by tuning the grading layer thickness and the low indium content InGaN layer thickness. In addition, as the ratios of grading layer to the low indium content InGaN layer increase, the emission peaks show redshift because the interband transitions energy became smaller.