Changsi Peng

Ordered nanostructures written directly by laser interference

We present a simplified method to employ laser interference lithography for the fabrication of ordered nanostructures. Neither resist, nor an elaborate fabrication process was needed. Four-beam interference patterns generated in this work included periodic arrays of holes in GaAs, covered with SiO(2) bubbles, and they were directly written into the sample. The diameters of the smallest holes were less than 30 nm. We propose a model to interpret the results.

Line defects in two-dimensional four-beam interference patterns

We have studied laser interference patterns, which consist of line defects on the surface of a GaAs substrate, generated by four-beam interference lithography. The orientation and periodicity of the defects are shown to depend on the configuration of the incident laser beams, while the widths of the defects are modified by varying the beam intensity. Influences of the phase and polarization on the simulated patterns are discussed.

Dilute nitride vertical-cavity surface-emitting lasers

A novel quaternary compound semiconductor material, Ga1 − xInxNyAs1 − y(0 < x, y < 1), was successfully used in demonstrating optically pumped continuous-wave vertical-cavity surface-emitting lasers emitting at 1280 nm. The epitaxial heterostructures of each laser wafer were grown in a single nucleation process by conventional molecular beam epitaxy using a nitrogen radio-frequency plasma source. The lasers consist of GaAs/AlAs distributed Bragg reflector mirrors and 6 or 15 Ga0.65In0.35N0.014As0.986/GaAs quantum wells with special strain-mediating layers. The laser characterization was carried out by using a fibre pigtailed 980 nm pump laser diode, 980/1300 nm wavelength division multiplexer and an optical spectrum analyser. A high optical output power of 3.5 mW was coupled lenslessly into a standard single-mode fibre.

Long-wavelength nitride lasers on GaAs

This paper reviews recent studies of structural and optical properties of long wavelength GaInNAs/GaAs quantum well semiconductors and the performance features of GaInNAs/GaAs vertical cavity surface emitting lasers (VCSELs) and edge-emitting lasers. The studies forecast that GaInNAs VCSELs and possibly edge-emitting lasers will become a compliment, or even a replacement, to the now dominant InP-based devices at 1.3-µm short-haul data transmission systems, but whether GaInNAs lasers in general will ever be competitive with the InP lasers at 1.4-1.6 µm is an entirely open issue today. The dilute nitride technology has still some distance to go in addressing its remaining concerns; yet, the authors believe that it is still the best bet to bring about the long-waited breakthrough in the component technology for optical fibre networks.

Quality inspection of nanoscale patterns produced by Laser Interference Lithography using image analysis techniques

This paper introduces the quality inspection of nanoscale patterns produced by the Laser Interference Lithography (LIL) technology using image analysis techniques. In this paper, patterns of two-beam and four-beam interferences are considered. Image analysis techniques based on the Hough transform (HT) and Maximum Likelihood Estimation (MLE) have been applied to detect and estimate various quality parameters for the two types of textures. The HT and a modified grey-scaled HT are introduced as a global approach for the analysis of the two-beam interference patterns. Surface parameters, such as the period, depth, and their uniformities, can be obtained directly without a priori knowledge of the textures. Due to different pattern structures and strong noise effects, the four-beam patterns are dealt with a different approach, using a statistical method based on the likelihood function to estimate each circles center and shape. Taking into consideration of noises and defects, another further rejection step is introduced to filter out noises and defects. Results from experimental samples are presented.

Diffusion at the interfaces of InGaNAs/GaAs quantum wells

Abstract Interdiffusion of the group-III atoms was interpreted for the structural and optical changes observed in X-ray diffraction and PL spectra of post-growth annealed 1.3-μm Ga 1− x In x N y As 1− y /GaAs material systems. Interdiffusion of As and N was observed to be much less than that of group-III in the temperature range studied in this work. A diffusion barrier, GaInNAs, grown on either side of the quantum well reduced interdiffusion very effectively. As a result, a blue shift of photoluminescence caused by annealing was prevented to a large extent, emission intensity was improved, and the spectra were shifted towards longer wavelengths, due to broader effective quantum wells. It was also found that interfacial stress tended to enhance diffusion.

System Requirement Analysis of Laser Interference Nanolithography

This paper presents a system requirement analysis of multi-beam laser interference nanolithography for nanoscale structuring of materials including seven sections: introduction, formation of multi-beam laser interference patterns, user requirements, system architecture, experiments, discussions and conclusions. Analytical expressions were obtained for the spatial distribution of radiation of the interfering beams as a function of their amplitudes, phases, angles of incidence on the sample, and polarization planes with computer simulation and experimental results. The environmental effect and technological potential were also discussed.

Interference lithography processes with high-power laser pulses

Laser interference lithography (LIL) is concerned with the use of interference patterns generated from two or several coherent beams of laser radiation for the structuring of materials. This paper presents the work on the processes based on resists and direct writing with laser interference lithography. In the work, a four-beam laser interference system was used as a submicrometer structuring tool in which a high-energy pulsed, frequency-tripled and TM polarized Nd:YAG laser (355 nm) with a coherent length of 3 m, energy power up to 320 mJ/cm2, pulse duration of 8 ns and 10 Hz repetition rate was used as a light source. The experimental results were achieved with 2-beam and 4-beam interference patterning. The processes can be used to define submicron surface relieves in large areas for use in the field of MEMS.

Formation of 4-beam laser interference patterns for nanolithography

This paper presents a theoretical analysis of formation of 4-beam laser interference patterns for nanolithography. Parameters of 4-beam interference patterns including the pattern amplitude, period, orientation and uniformity were discussed. Analytical expressions were obtained for the spatial distribution of radiation of the interfering beams as a function of their amplitudes, phases, angles of incidence on the sample, and polarization planes with computer simulation and experimental results.

High-gain InGaAsN materials

Beryllium was incorporated in InGaAsN single quantum well (SQW). Comparing with the conventional InGaAsN SQW structures, photoluminescence (PL) investigations show a significant improvement. After 3000 sec of annealing at 700 °C, the PL peak area is about 20 times higher while the wavelength keeps 25 nm longer. After 800 sec of this annealing, the PL quenched slowly for the conventional structures because of the strain relaxation, while the PL of the new structures increased rapidly and show no saturation after 3000 sec of annealing. Laser processing based on the new InGaAsN structures resulted in one half of the threshold current density compare to conventional InGaAsN.