Bae-Heng Tseng

Elimination of orientation domains and antiphase domains in the epitaxial films with chalcopyrite structure

Thin films of CuInSe2 and CuGaSe2 were grown by molecular‐beam epitaxy. Domain structures in these films were examined by transmission electron microscopy. We demonstrate that orientation domains may not form by the use of (001)GaAs substrate while antiphase domains can be eliminated by annealing the films in the presence of a Se beam. The annealing temperatures were 400 °C for CuInSe2 and 450 °C for CuGaSe2. Photoluminescence measurements on an annealed CuInSe2 film exhibited a decrease in intensity of optical emissions associated with antisite defects and an enhancement in near‐band‐edge emission intensity.

Surfactant modified growth of CuInSe2 thin films

Abstract A p-type film with resistivity as low as 0.05 Ω · cm and a mirror-like surface was obtained by the growth of the film in the presence of a Sb beam. The dramatic change in surface morphology is attributed to the layer-by-layer growth of the film. This film has a compact grain structure with grains about 1 mm in size, which is comparable with that of the Cu-rich film grown without Sb. A SIMS profile shows the segregation of Sb on the surface and a trace amount of Sb in the film. We also find that the sticking probabilities of the consituent atoms are affected by the addition of Sb during film growth.

Interface of CuIn1−xGaxSe2GaAs heterostructure

Abstract Misfit dislocations at the interface and a high density of threading dislocations initiated from the interface were observed in CuInSe2 epitaxial films grwon on (001) GaAs substrates at 475°C by a molecular beam epitaxy (MBE) technique. An epitaxial temperature as low as 300°C was realized by photo-assisted MBE or atomic layer epitaxy technique. Microtwins were found in the films grown by low-temperature processes. The difference in defect types in the films grown at different temperatures is attributed to the temperature dependence on the release of misfit strain in the films. A lattice-matched CuIn 0.3 Ga 0.7 Se 2 GaAs heterostructure grown at 520°C eliminates dislocations and microtwins. High-resolution lattice images show a contrast change at about 3 nm in thickness at the interface. By comparing the lattice image with a simulated one, we conclude that interdiffusion occurs during film growth.

Control of Defect Structures in CuGaSe 2 Epitaxial Films

An in-situ annealing process, which is conducted in the growth chamber by exposing the film to a Se beam immediately after film deposition, is developed to control defect structures in CuGaSe 2 epitaxial films. TEM observations showed that the films annealed at a temperature above 450°C could completely remove anti-phase domain boundaries and effectively annihilate threading dislocations. The annealing process also changes the distributions of intrinsic point defects in the film. Photoluminescence (PL) may reflect the microstructure improvement in the films. A suppress of the donor-to-acceptor transitions caused by antisite defects and an enhancement in the PL intensity were found in a annealed film.

Modification of surface and bandgap on Sb-incorporated CuInSe2 thin films by (NH4)2Sx sulfurization

In this work, we study the effect of the addition of antimony, and chemical sulfurization of CuInSe 2 thin films with (NH 4 ) 2 S X solution. CuInSe 2 thin films were deposited by the molecular beam deposition method and trace amounts of antimony have been added. The antimony, detected by scanning Auger electron microscopy, reacts with the bi- or tri-coordinated In to saturate the dangling bonds on the growing surface as surfactants. During (NH 4 ) 2 S X sulfurization, the sulfur atoms enter the thin films through a pathway which is created by the replacement of antimony atoms segregated on the thin film surface. A portion of the selenide film is transformed into an alloy of CuInSe 2 and CuInS 2 on the grain surface. Significant amounts of sulfur (35%) distributed throughout the thin film of CuInSe 2 under an antimony source temperature of 510°C in the film growth was shown from the Auger electron depth profile, and an increase of energy bandgap up to 1.3 eV as determined from optical absorption measurements. The chemical reactions are justified from thermodynamic considerations.