KEYWORDS: Vertical cavity surface emitting lasers, Mirrors, Reflectivity, Resonators, Resistance, Near field diffraction, Transmittance, Lithium, Light sources, High power lasers
For the past years, ArF immersion has been employed as the major lithography tool in the foundry manufacturing to fabricate the patterns of minimum pitch and size. However, for semiconductor scaling beyond N7 the application of EUV lithography is considered to be crucially important to overcome the physical limitation of ArF immersion and to realize even smaller patterns. In the case of ArF photo processes, the best mask size for a specific pitch could be selected with the consideration of optical performances such as NILS, MEEF, etc. In contrast, for the EUV processes the optical and resist stochastic effect should also be taken into account as an important factor in deciding the best mask size. In this paper, we are going to discuss the dose and mask size optimization process for an DRAM contact hole layer with EUV lithography utilizing stochastic simulations; this contains also the stochastic response of the resist. In order to calibrate a predictive stochastic resist model, which is required for this application, measurements of the stochastic resist response are necessary. In addition, the systematic and stochastic errors of CD-SEM measurements have to be estimated. We will compare experimentally obtained NILS and MEEF to simulated results, which are in very good agreement. Also, we show a comparison of experimental and computational analysis of LCDU (Local CD Uniformity).
The band structure, density of states, optical properties, effective masses and loss function of AlxGa1−xAs and InyGa1−yAs were performed by the first-principles method within the local density approximation. The calculated direct band gap of the AlAs, Al0.5Ga0.5As, GaAs, In0.5Ga0.5As and InAs were 1.608 eV, 1.34eV, 1.02eV, 0.646eV and 0.316eV at G point, which were direct bandgap semiconductor materials. In addition, dielectric functions, the absorption function, refractive index, loss function and effective mass were analyzed in detail. The effective masses of AlxGa1−xAs and InyGa1−yAs were small, so they have high carrier mobility. These results make them to be promising candidates for future electronics.
GaN-based high-power laser diodes (LDs) have attracted tremendous interests in next-generation lighting applications, such as laser display, car laser light. However, high injection current usually brings inevitable drawbacks, including the well-known efficiency droop, Auger recombination and self-heating which obstruct further improvements of GaN-based optoelectrical devices. In this paper, influence of hole overflow at high injection current in an asymmetric GaN-based highpower blue LD has been comprehensively investigated and successfully suppressed by employing a new sandwiched GaN/AlGaN/GaN lower quantum barrier (GAG-LQB). Systematical simulations and measurements of structural and optical properties are carried out. As a result, the V-shaped defects induced by thick n-InGaN waveguide layer are apparently eliminated, which provides a more growth-friendly platform for deposition of the rest epitaxial layers and thus a better crystalline quality is obtained. On the other hand, the modified LD exhibits better photo-electrical properties with slope efficiency (SE) increasing from 0.98 to 1.24 and wall-plug efficiency (WPE) increasing from 18.7% to 20.5% at a high current of 1.5 A and no obvious efficiency droop is observed at a current as high as 2 A compared with the conventional one, because the middle-inserted AlGaN layer could form an extra barrier on the valence band to weaken the hole overflow and enhance the radiative recombination. Furthermore, the in-plane compressive strain induced by InGaN quantum wells (QWs) is also partially compensated by the tensile strain induced by the AlGaN layer. Therefore, the piezoelectric fieldinduced polarization is effectively alleviated and the wavelength blueshift is reduced from 7 nm to 1.6 nm.
The blue laser diode (LD) illuminator in this study was composed of a cerium doped yttrium aluminum garnet (Ce:YAG) crystal, a 450-nm laser diode and an optical fiber. After a first-principles calculation, the energy gap of the Ce:YAG crystal was found to be 4.71 eV, which was less than that of the YAG. The luminescent properties of the Ce:YAG were determined by the electronic distribution of the Ce (d) and Ce (f) orbits. The Ce:YAG crystal had two characteristic absorption peaks of Ce3+ at 332 nm and 455 nm. Hence, the 450-nm LD excited fluorescence spectra of a Ce:YAG crystal can be used for laser illumination. We discovered that the luminous efficiency of the LD increased with increasing color temperature for 4000 K, 5000 K, 6000 K and 6500 K but not for 3500 K, due to the low light transmittance of the thickest Ce:YAG crystal. The highest color-rendering index was about 70.0. Also, the blue laser without the 430-nm light from spectral radiance was, compared to an LED, a more serious eye hazard. We calculated that the permissible exposure time of the LD was longer than that of an LED. We also discovered that LD illumination is more secure than LED illumination.
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