Bijun Zhao

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.

Reduced Droop Effect in Nitride Light Emitting Diodes With Taper-Shaped Electron Blocking Layer

A taper-shaped AlGaN electron blocking layer (TEBL) has been designed and incorporated in InGaN/GaN light emitting diodes (LEDs) to promote hole injection and electron confinement under high current injection conditions. Fabricated LEDs with a TEBL exhibit reduced operating voltage, enhanced efficiency as well as alleviated droop effect, compared with those with a conventional bulk AlGaN EBL. The improvement is due to improved electron confinement and hole transportation as well as decreased electrostatic fields in the active region.

Enhanced performance of InGaN/GaN based solar cells with an In(0.05)Ga(0.95)N ultra-thin inserting layer between GaN barrier and In(0.2)Ga(0.8)N well.

The effect of ultra-thin inserting layer (UIL) on the photovoltaic performances of InGaN/GaN solar cells is investigated. With UIL implemented, the open-circuit voltage was increased from 1.4 V to 1.7 V, short-circuit current density was increased by 65% and external quantum efficiency was increased by 59%, compared to its counterparts at room temperature under 1-sun AM1.5G illumination. The improvements in electrical and photovoltaic properties are mainly attributed to the UIL which can boost the crystal quality and alleviate strain. Moreover, it can act as a transition layer for higher indium incorporation and an effective light sub-absorption layer in multiple quantum wells.