Abstract
The features of eight-period In0.2Ga0.8N/GaN quantum wells (QWs) with silicon (Si) doping in the first two to five quantum barriers (QBs) in the growth sequence of blue light-emitting diodes (LEDs) are explored. Epilayers of QWs’ structures are grown on 20 pairs of In0.02Ga0.98N/GaN superlattice acting as strain relief layers (SRLs) on patterned sapphire substrates (PSSs) by a low-pressure metal-organic chemical vapor deposition (LP-MOCVD) system. Temperature-dependent photoluminescence (PL) spectra, current versus voltage (I-V) curves, light output power versus injection current (L-I) curves, and images of high-resolution transmission electron microscopy (HRTEM) of epilayers are measured. The consequences show that QWs with four Si-doped QBs have larger carrier localization energy (41 meV), lower turn-on (3.27 V) and breakdown (− 6.77 V) voltages, and higher output power of light of blue LEDs at higher injection current than other samples. Low barrier height of QBs in a four-Si-doped QB sample results in soft confinement potential of QWs and lower turn-on and breakdown voltages of the diode. HRTEM images give the evidence that this sample has relatively diffusive interfaces of QWs. Uniform spread of carriers among eight QWs and superior localization of carriers in each well are responsible for the enhancement of light output power, in particular, for high injection current in the four-Si-doped QB sample. The results demonstrate that four QBs of eight In0.2Ga0.8N/GaN QWs with Si doping not only reduce the quantum-confined Stark effect (QCSE) but also improve the distribution and localization of carriers in QWs for better optical performance of blue LEDs.
Highlights
Silicon (Si) doping in GaN quantum barriers (QBs) can kindle Coulomb screening of polarization field and cause suppression of quantum-confined Stark effect (QCSE) in InGaN/GaN quantum wells (QWs)
Si doping in proper thickness and numbers of QBs in InGaN/GaN QWs is crucial for further promotion of brightness and efficiency of InGaN blue light-emitting diodes (LEDs) operating at high injection current
The results demonstrate that the sample with the first four QBs containing Si doping has relatively lower barrier height and larger localization energy of carriers which is evidenced by diffusive interfaces of QWs in high-resolution transmission electron microscopy (HRTEM) images
Summary
Silicon (Si) doping in GaN quantum barriers (QBs) can kindle Coulomb screening of polarization field and cause suppression of quantum-confined Stark effect (QCSE) in InGaN/GaN quantum wells (QWs). The favorable periods and thickness of InGaN/GaN QWs for high brightness and high EQE under high injection current (above several tens of mA) of blue LEDs are reported [16,17,18]. The best optical and electrical performances of blue LEDs are demonstrated if the active region consists of 12 periods of InGaN/GaN QWs at the injection current 42 A/cm2 [17]. We present the optical, electrical, and material characteristics of eightperiod In0.2Ga0.8N/GaN QWs with first two to five QBs in the growth sequence possessing Si doping of blue LEDs. The results give a deeper insight into the mechanisms of carrier localization, confinement potential, and QCSE of QWs on luminescence behaviors of blue LEDs under high injection current
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