Institute of Electron Technology

Agreement is found between the experimentally and theoretically determined branch point level for ZnO located (2.7 ± 0.1) eV above the valence band maximum. This result is obtained on the basis of a combined study where its experimental position is extracted from temperature‐dependent capacitance versus voltage measurements on AZO/n‐Zn(1−x)MgxO:Al/SiOx/p‐Si heterostructures with Mg content equal to ≈0.07 and ≈0.23 combined with transmission electron microscopy and ellipsometry measurements to assess the SiOx interlayer contribution. This analysis confirms the values previously published in Schifano et al. J. Appl. Phys. 136, 245304 (2024). In contrast, density‐functional theory calculations are used for obtaining the theoretical estimates. A similar comparison, in the MgO case, reveals a difference of ≈0.6 eV between the theoretically predicted and experimentally obtained values placed (4.3 ± 0.1) and (3.7 ± 0.4) eV above the valence band maximum, respectively. In this case, the assumption of a linear variation of the ZnMgO branch‐point level between the two binary compounds, ZnO and MgO, used for the extraction of the experimental value, is among the probable causes of the residual difference found. Overall, the presented results indicate that the whole set of p(O) related valence bands should be included for a precise determination of the branch point energies if ab‐initio methods are used.

Atomic force microscopy enables three-dimensional high-resolution imaging of surfaces with nanoscale features. In order to obtain the quantitative information about surface geometry, the atomic force microscope’s scanning system must be calibrated. This is usually done by using calibration samples of known and/or defined shape based on either lithographic or crystal structures. In this work we report on a microelectromechanical device, referred to as a displacement generator, whose vertical deflection is controlled electronically. The designed, fabricated and applied device is formed out of a silicon nitride doubly clamped lever, referred to as a microbridge, with a deposited pair of platinum strips. When the MEMS displacement generator is immersed in a magnetic field and when it is electrically biased, the associated Lorentz force induces a structural displacement. In the presented design, the silicon nitride microbridges were fabricated on a (110) silicon wafer in a Wheatstone bridge configuration. A second reference cantilever was mechanically supported by the silicon substrate. In this way, a highly symmetrical structure was fabricated, making it possible to control precisely deflection in Z direction with sub-nanometre precision. The cantilever’s high resonance frequency, of ca. 500 kHz, makes the constructed device insensitive to external vibration sources which are typically at much lower frequencies. As the stage function can be described using the simple harmonic oscillator model, it is clear that the system can operate with sub-nanometre resolution, which, for the purpose of microscope calibration, is extremely beneficial. By placing of the atomic force microscope tip on the actuated reference device it is possible to determine the response of the system over a wide frequency bandwidth. In this work we will describe the fabrication process of the MEMS displacement generator, interferometric and traceable investigations of thermomechanical and electromagnetic actuation schemes. Moreover, we will present the results of the calibration of an atomic force microscope operating in contact and intermittent contact modes.

High contrast gratings (HCGs) are diffraction gratings whose period is less than the wavelength of light, made of a material with a high refractive index. Monolithic HCGs (MHCGs) are made of the same material as the cladding. They can be made of almost any material used in optoelectronics. We show experimentally and via simulations that shaping the cross-section of the MHCG stripes enables very broad high reflection spectrum.

The precise determination of carrier concentration in doped semiconductor materials and nanostructures is of high importance. Many parameters of an operational device are dependent on the proper carrier concentration or its distribution in both the active area as well as in the passive parts as the waveguide claddings. Determining those in a nondestructive manner is, on the one hand, demanded for the fabrication process efficiency, but on the other, challenging experimentally, especially for complex multilayer systems. Here, we present the results of carrier concentration determination in In0.53Ga0.47As layers, designed to be a material forming quantum cascade laser active areas, using a direct and contactless method utilizing the Berreman effect, and employing Fourier-transform infrared (FTIR) spectroscopy. The results allowed us to precisely determine the free carrier concentration versus changes in the nominal doping level and provide feedback regarding the technological process by indicating the temperature adjustment of the dopant source.

In this work, two-section, coupled cavity, mid-IR quantum cascade lasers (QCLs) were characterized in terms of their tuning range and emission stability under operation towards potential application in detection systems. Devices were processed by inductively coupled plasma reactive ion etching (ICP-RIE) from InP-based heterostructure, designed for emission in the 9.x micrometer range. Single mode devices were demonstrated with a better than 20 dB side mode suppression ratio (SMRS). The fabrication method resulted in improved yield, as well as high repeatability of individual devices. Continuous, mode-hop-free tuning of emission wavelength was observed across ~4.5 cm−1 for the range of temperatures of the heat sink from 15 °C to 70 °C. Using the thermal perturbation in the lasing cavity, in conjunction with controlled hopping between coupled-cavity (CC) modes, we were able to accomplish tuning over the range of up to ~20 cm−1.

980 nm VCSELs with different numbers of top dielectric DBR periods added to a 5.5-period top semiconductor DBR and with various oxide aperture diameters are investigated to determine the impact of the added dielectric DBR’s impact on the static and dynamic properties of the VCSELs. For VCSELs with the same oxide aperture diameter we observe smaller small-signal modulation bandwidth and lower D-factor for the VCSELs with more pairs of dielectric DBRs. For the VCSELs with 4 μm oxide aperture diameters with 8 and 12 periods of added top dielectric DBRs we measured bandwidths of 29 and 26 GHz, respectively.

The effect of recrystallization of 99.3Sn–0.7Cu wt. % solder alloy on the allotropic transition of β to α-Sn (so-called tin pest phenomenon) was investigated. Bulk samples were prepared, and an InSb inoculator was mechanically applied to their surfaces to enhance the transition. Half of the samples were used as the reference material and the other half were annealed at 180 °C for 72 h, which caused the recrystallization of the alloy. The samples were stored at −10 and −20 °C. The β-Sn to α-Sn transition was monitored using electrical resistance measurements. The expansion and separation of the tin grains during the β-Sn to α-Sn transition process were studied using scanning electron microscopy. The recrystallization of the alloy suppressed the tin pest phenomenon considerably since it decreased the number of defects in the crystal structure where heterogeneous nucleation of β-Sn to α-Sn transition could occur. In the case of InSb inoculation, the spreading of the transition towards the bulk was as fast as the spreading parallel to the surface of the sample.