Temperature and excitation dependence of stimulated emission and spontaneous emission in InGaN epilayer

Temperature and excitation dependent photoluminescence(PL) of InGaN epilayer grown on c-plane Ga N/sapphire template by molecular beam epitaxy(MBE) has been systematically investigated. The emission spectra of the sample consisted of strong multiple peaks associated with one stimulated emission(SE) located at 430 nm and two spontaneous emissions(SPE) centered at about 450 nm and 480 nm, indicating the co-existence of shallow and deep localized states.The peak energy of SE exhibiting weak s-shaped variation with increasing temperature revealed the localization effect of excitons. Moreover, an abnormal increase of the SPE intensity with increasing temperature was also observed, which indicated that the carrier transfer between the shallow and deeper localized states exists. Temperature dependent time-resolved PL(TRPL) demonstrated the carrier transfer processes among the localized states. In addition, a slow thermalization of hot carriers was observed in InGaN film by using TRPL and transient differential reflectivity, which is attributed to the phonon bottleneck effect induced by indium aggregation.

Boron-rich layer removal and surface passivation of boron-doped p–n silicon solar cells

In boron-doped p+-n crystalline silicon(Si) solar cells, p-type boron doping control and surface passivation play a vital role in the realization of high-efficiency and low cost pursuit. In this study, boron-doped p+-emitters are formed by boron diffusion in an open-tube furnace using borontribromide(BBr3) as precursor. The formed emitters are characterized in detail in terms of shape of the doping profile, surface doping concentration, junction depth, sheet resistance and removal of the boron-rich layer(BRL). In the aspect of BRL removal, three different methods were adopted to investigate their influence on device performance. The results demonstrate that our proposed chemical etch treatment(CET) with the proper etching time could be an effective way to remove the BRL.After removal of the BRL, Al_2 O_3/SiN_x stacks are deposited by atomic layer deposition(ALD) and plasma-enhanced chemical vapor deposition(PECVD) to passivate the cell surface. It was found that a reasonably-high implied Voc of 680 mV has been achieved for the fabricated n-type Si solar cells.

Multifunctional polyethyleneimine for synthesis of core-shell nanostructures and electrochemiluminescent detection of three AMI biomarkers

Simplicity and stability of an analytical method are the key to practical applications.In order to achieve such a goal,a molecule with multifunction could be one of the strategies.In this work,the multifunctional characteristics of branched polyethylenemine(bPEI)were employed for verification of this hypothesis.Three types of amines in the bPEI can be used to synthesize core-shell nanostructures(bPEI@Au and SiO_(2)@bPEI@Au)in a simple one-pot process within 1 h,and as coreactants with over 500-fold enhancement for electrochemiluminescent(ECL)detection.Based on the remarkable performance of bPEI,a label-free ECL immunosensor and its array with the same assembly strategy were constructed for the simple and rapid determination of three acute myocardial infarction(AMI)biomarkers:cardiac troponin I(cTnI),human-type fatty acid binding protein(hFABP)and copeptin.Both methods exhibited excellent stability and sensitivity with wide linear range and low limits of detection down to fg/mL level by the photomultiplier tube and pg/mL level by the electron-multiplying charge-coupled device.

GaN-based ultraviolet microdisk laser diode grown on Si

This work reports a demonstration of electrically injected GaN-based near-ultraviolet microdisk laser diodes with a lasing wavelength of 386.3 nm at room temperature. The crack-free laser structure was epitaxially grown on Si substrates using an Al-composed down-graded Al N/AlGaN multilayer buffer to mitigate the mismatches in the lattice constant and coefficient of thermal expansion, and processed into “sandwich-like” microdisk structures with a radius of 12 μm. Air-bridge electrodes were successfully fabricated to enable the device electrical characterization. The electrically pumped lasing of the as-fabricated microdisk laser diodes was evidenced by the rapid narrowing down of electroluminescence spectra and dramatic increase in the light output power, as the current exceeded the threshold of 248 mA.