ABSTRACT
The influence of growth interruption on the surface and luminescence properties of AlGaN/GaN ultraviolet multi-quantum wells (UV MQWs) is investigated. It is found that when the well and barrier layers of MQW samples are continuously grown at the same temperature, they have lower edge dislocation density and flatter surface of MQWs compared to samples with interrupted well and barrier growth. Moreover, continuous growth of well and barrier layers is more conducive to improving the luminescence efficiency of MQWs. This phenomenon is attributed to more impurity incorporation induced by the growth interruption, while a continuous growth of well and barrier can reduce surface diffusion and migration processes of atoms, reducing the defects and surface roughness of MQWs. In addition, the continuous growth of well and barrier can better control the reaction between Al and N atoms, avoiding the formation of excessively high Al content AlGaN at the well/barrier interface, thus improving the luminescence of UV MQWs.
ABSTRACT
We have observed the transient behavior in the AlGaN photoluminescence. Under an excitation of 325 nm He-Cd laser beam, the blue luminescence (BL) bands and yellow luminescence (YL) bands of AlGaN vary with increasing illumination time. We propose that the chemical reactions between BL-related CNON-Hi (CN-Hi) and YL-related CN-Hi (CN) defect states are the cause of such a phenomenon. The BL transition temperature (Tt) is defined as the temperature at which the intensity of BL bands induced by CNON-Hi is equal to that originated from CN-Hi. Only at Tt, BL shows a peak energy variation due to the exposure. The Tt of AlGaN is higher than what is similarly detected in GaN because of the high reactivity of Al to O.
ABSTRACT
[This corrects the article DOI: 10.3389/fonc.2021.629974.].
ABSTRACT
Temperature characteristics of near-UV laser diodes (LDs) with a lasing wavelength of 384â nm are investigated. The characteristic temperature of threshold current (T0) of the UV LDs is low. Thus, the performance of the UV LDs under continuous wave (CW) operation is not as good as under pulsed operation especially at a high injection current. In addition, it is found that self-heating is a key factor for CW characteristics of the UV LDs, where suppression of the self-heating by using thick waveguide layers can increase the critical current of thermal rollover of the UV LD's operation. A high CW output power of 2.0â W is achieved for an InGaN near-UV LD with the n-side down on a sub-mount, whose threshold current density is 1.27â kA/cm2 and the highest wall plug efficiency (WPE) is approximately 15.9% at an injection current of 1.2â A.
ABSTRACT
The major obstacle to treat cervical squamous cell carcinoma (CSCC) is the high prevalence of metastasis, which severely affects 5-year survival rate and quality of life for cancer patients. The DEAD-box helicase family has been reported to be a critical mediator in the development and metastasis of various cancers. DEAD-box helicase 19A (DDX19A) is a member of the DEAD-box helicase family; however, its functional role in CSCC is unclear. In this study, bioinformatics analysis of clinical samples from public databases demonstrated that the expression of DDX19A was elevated in CSCC tissues and that high expression of DDX19A was positively correlated with metastasis and poor clinical outcome. Functionally, we found that DDX19A promoted CSCC cell migration and invasion in vitro and lung metastasis in vivo. Mechanistically, overexpression of DDX19A increased NADPH oxidase 1 (NOX1) expression, enhanced reactive oxygen species (ROS) production, and induced the migration and invasion of CSCC cells. Rescue experiments revealed that DDX19A-induced CSCC functional alterations were dependent on NOX1 and that DDX19A-promoted CSCC metastasis was abrogated upon the inhibition of ROS. Our results demonstrated that DDX19A could promote CSCC metastasis by inducing NOX1-mediated ROS production and that blockage of the NOX1/ROS axis might serve as a potential therapeutic target for patients with DDX19A-overexpressed CSCC.
ABSTRACT
Yellow Luminescence (YL) band and blue luminescence (BL) band in a studied unintentionally doped GaN sample show a transient behaviour where the observed luminescence intensities change with the exposure time of the sample under 325 nm laser beam excitation at 10-300 K. Such an intensity variation is accompanied with a red-shift for YL peak at 10-140 K and one for BL peak at 140 K. We propose that such behaviours are related to the chemical transformations of YL-related CN and CNON defects, and BL-related CN-Hi and CNON-Hi defects during the exposure.
