Defeng Lin

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.

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.

Simulation of electrical properties of InxAl1—xN/AlN/GaN high electron mobility transistor structure

Electrical properties of InxAl1—xN/AlN/GaN structure are investigated by solving coupled Schrodinger and Poisson equations self-consistently. The variations in internal polarizations in InxAl1—xN with indium contents are studied and the total polarization is zero when the indium content is 0.41. Our calculations show that the two-dimensional electron gas (2DEG) sheet density will decrease with increasing indium content. There is a critical thickness for AlN. The 2DEG sheet density will increase with InxAl1—xN thickness when the AlN thickness is less than the critical value. However, once the AlN thickness becomes greater than the critical value, the 2DEG sheet density will decrease with increasing barrier thickness. The critical value of AlN is 2.8 nm for the lattice-matched In0.18Al0.82N/AlN/GaN structure. Our calculations also show that the critical value decreases with increasing indium content.

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.