Yian Yin

Advantages of GaN based light-emitting diodes with a p-InGaN hole reservoir layer

A p-type InGaN hole reservoir layer (HRL) was designed and incorporated in GaN based light-emitting diodes (LEDs) to enhance hole injection efficiency and alleviate efficiency droop. The fabricated LEDs with p-type HRL exhibited higher light output power, smaller emission energy shift and broadening as compared to its counterpart. Based on electrical and optical characteristics analysis and numerical simulation, these improvements are mainly attributed to the alleviated band bending in the last couple of quantum well and electron blocking layer, and thus better hole injection efficiency. Meanwhile, the efficiency droop can be effectively mitigated when the p-InGaN HRL was used.

Performance enhancement of blue light-emitting diodes without an electron-blocking layer by using special designed p-type doped InGaN barriers

In this study, the characteristics of the nitride-based blue light-emitting diode (LED) without an electron-blocking layer (EBL) are analyzed numerically. The emission spectra, carrier concentrations in the quantum wells (QWs), energy band diagrams, electrostatic fields, and internal quantum efficiency (IQE) are investigated. The simulation results indicate that the LED without an EBL has a better hole-injection efficiency and smaller electrostatic fields in its active region over the conventional LED with an AlGaN EBL. The simulation results also show that the LED without an EBL has severe efficiency droop. However, when the special designed p-type doped InGaN QW barriers are used, the efficiency droop is markedly improved and the electroluminescence (EL) emission intensity is greatly enhanced which is due to the improvement of the hole uniformity in the active region and small electron leakage.

Enhanced Performance of Blue Light-Emitting Diodes With InGaN/GaN Superlattice as Hole Gathering Layer

An InGaN/GaN superlattice (SL) with Mg-doped barriers was designed and inserted into the InGaN-based blue light-emitting diodes (LEDs) as a hole gathering layer (HGL) to promote hole injection into the active region. The fabricated LEDs with the SL HGL show 36.4% increase in light output power at an injection current of 200 mA. Meanwhile, the efficiency droop is also mitigated effectively, as compared to the traditional LEDs. The improved performance is attributed to increased hole injection efficiency and decreased electron leakage into the p-type region.

Performance Enhancement of Near-UV Light-Emitting Diodes With an InAlN/GaN Superlattice Electron-Blocking Layer

In this study, the characteristics of the nitride-based near-UV light-emitting diode (LED) with an InAlN/GaN superlattice (SL) electron-blocking layer (EBL) are analyzed numerically and experimentally. The emission spectra, carrier concentrations in the quantum wells, energy-band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results indicate that the LED with an InAlN/GaN SL EBL has a better hole-injection efficiency and lower electron leakage over the LED with a conventional rectangular AlGaN EBL or with an AlGaN/GaN SL EBL. The results also show that the efficiency droop is markedly improved when the InAlN/GaN SL EBL is used.

Study of InGaN/GaN Light Emitting Diodes With Step-Graded Electron Blocking Layer

Step-graded AlGaN electron blocking layers (EBLs) have been designed to replace the original AlGaN EBL in blue light emitting diodes (LEDs). The step-graded EBL with increasing Al composition along the growth direction (IEBL) leads to inferior optical performance in the fabricated LEDs, whereas the step-graded EBL with decreasing Al composition (DEBL) results in enhanced light output power and reduced efficiency droop, compared with the original EBL. The simulation results indicate enhanced hole injection and electron confinement by DEBL, which accounts for improved performance. On the contrary, insufficient electron blocking and hole injection by IEBL lead to inferior performance.

The advantage of blue InGaN multiple quantum wells light-emitting diodes with p-AlInN electron blocking layer

InGaN based light-emitting diodes (LEDs) with different electron blocking layers have been numerically investigated using the APSYS simulation software. It is found that the structure with a p-AlInN electron blocking layer showes improved light output power, lower current leakage, and smaller efficiency droop. Based on numerical simulation and analysis, these improvements of the electrical and optical characteristics are mainly attributed to the efficient electron blocking in the InGaN/GaN multiple quantum wells (MQWs).

Improved performance of near UV light-emitting diodes with a composition-graded p-AlGaN irregular sawtooth electron-blocking layer*

We investigate the performances of the near-ultraviolet (about 350 nm–360 nm) light-emitting diodes (LEDs) each with specifically designed irregular sawtooth electron blocking layer (EBL) by using the APSYS simulation program. The internal quantum efficiencies (IQEs), light output powers, carrier concentrations in the quantum wells, energy-band diagrams, and electrostatic fields are analyzed carefully. The results indicate that the LEDs with composition-graded p-Al x Ga1−x N irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs. The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface, which results in less electron leakage and better hole injection efficiency, thus reducing efficiency droop and enhancing the radiative recombination rate.

Improvement of the crystal quality of AlInN by using the patterned sapphire substrate

Lattice-matched (x =0.18) AlxIn1− xN epilayers were grown on GaN/ patterned sapphire substrate (PSS ) (0 0 0 1) and GaN/ unpatterned sapphire substrate (UPSS) (0 0 0 1) by metal-organic chemical vapor deposition (MOCVD). The quality of the grown AlInN epilayers on the PSS and UPSS were compared. Structural characteristics and surface morphology optical properties of the AlInN epilayers were investigated using double crystal X-ray diffraction (DCXRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). It is seen from the DCXRD rocking spectrum that the full width at half maximum (FWHM) of the AlInN grown on PSS was 260 arcsec which is less than UPSS value. The lower value of FWHM indicates that the crystalline quality of the AlInN epilayers grown on PSS is improved compared to AlInN grown on UPSS. It is slso clearly seen from the AFM images that the dislocation density and root mean square (RMS)is less for the AlInN grown on PSS. The above results indicate that the PSS could improve the crystalline and surface morphology greatly.