Qingwen Deng

An investigation on InxGa1−xN/GaN multiple quantum well solar cells

The conversion efficiency of InxGa1−xN/GaN multiple quantum well solar cells is originally investigated in theory based on the ideal diode model and the ideal unity quantum well model. The results reveal that the conversion efficiency partially depends on the width of the quantum well and the thickness of the barrier region but is dominated by the number of quantum wells and indium content of InxGa1−xN. The calculated results are found to be basically trustworthy by comparing with reported experimental results. An In0.15Ga0.85N/GaN multiple quantum well solar cell is successfully fabricated with a conversion efficiency of 0.2%. The main discrepancy between calculated and experimental results is the material quality and manufacturing technology which need to be improved.

Enhanced performance of InGaN/GaN multiple quantum well solar cells with patterned sapphire substrate

In this paper, the enhanced performance of InGaN/GaN multiple quantum well solar cells grown on patterned sapphire substrates (PSS) was demonstrated. The short-circuit current (Jsc) density of the solar cell grown on PSS showed an improvement of 60%, compared to that of solar cells grown on conventional sapphire substrate. The improved performance is primarily due to the reduction of edge dislocations and the increased light absorption path by the scattering from the textured surface of the PSS. It shows that the patterned sapphire technology can effectively alleviate the problem of high-density dislocations and low Jsc caused by thinner absorption layers of the InGaN based solar cell, and it is promising to improve the efficiency of the solar cell.

Influence of electric field on persistent photoconductivity in unintentionally doped n-type GaN

The influence of electric field on persistent photoconductivity in unintentionally doped n-GaN is investigated. It was found that under higher electric field the build-up course was slowed down while the decay course was accelerated. After a higher-voltage pulse, it was observed that the current dropped to a value lower than the dark current, and a current increase that lasted for thousands of seconds was observed. It is suggested that the above phenomena should be caused by the increase in capture rate of electron traps with electric field and are related to the Coulomb-repulsive characteristic of defects related to persistent photoconductivity.

Comparison of as-grown and annealed GaN/InGaN:Mg samples

Mg-doped InGaN was grown on unintentionally doped GaN layer, and Mg and defect behaviours in both GaN and InGaN?:?Mg were investigated through photoluminescence measurement at 7?K. Mg acceptor was found in unintentionally doped GaN after thermal annealing in N2 ambient, and Mg activation energy was estimated to be 200?meV and 110?meV for GaN and InGaN, respectively. Particularly, the ultraviolet band (3.0?3.2?eV) in the GaN layer was infrequently observed in the unannealed sample but quenched in the annealed sample; this band may be associated with oxygen-substituted nitrogen defects. Moreover, the measurement errors of photoluminescence and x-ray diffraction originated from strain were taken into account.

Behavioural investigation of InN nanodots by surface topographies and phase images

We employ surface topographies and phase images to investigate InN nanodots. The samples are annealed at 450, 500 and 550 . The results reveal that the statistical distributions of number density and mean size depend on annealing ambient. The behaviours of thermal annealing between InN films and InN nanodots are distinguishable: the alloying process of InN and GaN not only occurs in InN platelets, but also in InN nanodots once the samples are annealed at the growth temperature of InN nanodots, while the main change in InN films is the decomposition of InN into In droplets and N2.