Alina Maksimova

In this work, the physical origin of the persistent photoconductivity (PPC) effect in InP films synthesized by plasma-enhanced atomic layer deposition (PE-ALD) at 380 °C was investigated. Cross-sectional TEM confirmed the formation of a nanocrystalline cubic InP layer on Si, while Raman spectroscopy revealed comparable crystalline characteristics for films grown on Si and fused silica substrates. The photocurrent relaxation kinetics was well described by a stretched-exponential function, indicating a broad distribution of characteristic relaxation times associated with heterogeneous trapping and recombination processes. A significant difference was revealed between the activation energy of equilibrium electron transport (0.114 ± 0.003 eV) and the macroscopic recombination barrier for nonequilibrium carriers (0.270 ± 0.058 eV). Hall-effect measurements showed that the PPC is predominantly associated with an increase in electron concentration, rather than changes in carrier mobility. The long lifetime of the photoexcited state is consistent with a barrier-mediated mechanism of spatial separation of electron hole pairs associated with grain boundaries.

The fabrication of periodical GaN/InP structures on Si with a wide layer thickness variation (from submonolayer digital alloys to multilayer stacks) using low-temperature plasma technology is explored in the paper. The proposed technology, which combines the approaches of plasma-enhanced chemical vapor deposition (PECVD) and atomic-layer deposition, was realized at 380 °C using a standard capacitively coupled plasma PECVD reactor. Trimethylindium, trimethylgallium, phosphine, and nitrogen (N2) were used as sources of In, Ga, P, and N, respectively. A series of GaN/InP periodical structures were grown on an Si (001) substrate with a previously deposited thin (7 nm) GaP buffer layer. A structure grown as submonolayer digital alloys (a short-period superlattice with GaN and InP thicknesses of 0.3 and 0.6 nm) exhibits a crystal structure consisting of both microcrystalline and epitaxially oriented grains that follow the orientation of the Si substrate. The vertical size of the grains corresponds to the total GaN/InP periodical structure’s thickness. However, with an increase in the GaN barrier layer thickness to 1.5–3 nm, the GaN undergoes amorphization. This leads to the formation of a layered structure containing misoriented nanocrystalline InP layers embedded between amorphous GaN layers. This effect is associated with significant incorporation of phosphorus into GaN layers, which are formed using a N2 + H2 gas mixture plasma. Indeed, the H2 plasma used for GaN deposition interacts with the phosphorus deposited on the chamber wall during the previous InP step. The discovered issue should be taken into account for plasma technology development of multilayer structures, which included a combination of III-nitride/III-phosphide.

Light emitting diodes (LEDs) based on III-V semiconductors are in a great demand for many appli cations and tend to be miniaturized. However, with downscaling of planar LEDs, the surface states on the structure sidewalls, acting as nonradiative recombination centers, begin to play a significant role and deteriorate the device performance. The transition from planar to nanowire-based geometry helps to overcome this limitation. Here, we introduce a bottom-up microLED structure based on epitaxial GaP/GaAsPN/GaP nanowire arrays grown on low-cost Si(111) wafers. The active region demonstrates bright photoluminescence in the red spectral region while the radial p-i-n structure allows for electrical pumping. The opto-electrical characteristics and performance of the suggested microLEDs remain with the miniaturization of devices down to microscale equivalent lateral size. Moreover, we didn’t observe an efficiency cliff even for current density exceeding 300 A/cm². The proposed architecture paves the way to a new generation of nanowire-based microLEDs.

Boron phosphide (BP) thin films are potential selective contact layers for photovoltaic (PV) devices. However, lower deposition temperatures are preferred in the fabrication of many PV devices, such as solar cells, to reduce their cost. Here, boron phosphide layers were grown on silicon (100) substrates using the standard plasma-enhanced chemical vapor deposition (PECVD) and time-modulated PECVD methods with trimethylboron [B(CH3)3, TMB] and phosphine precursors. The effect of plasma power and Ar addition on structural properties and chemical composition is investigated, while material properties are analyzed by transmission electron microscopy. Chemical characterization by the electron diffraction x-ray spectroscopy method showed high carbon content in the BP layer. Electron energy loss spectroscopy demonstrated almost stoichiometric B and P (1:1) content. Raman spectroscopy of annealed samples showed an increase in carbon-related peaks, therefore indicating that annealing does not lead to the crystallization of boron phosphide. Thus, using TMB as a precursor of boron leads to carbon contamination in both standard and time-modulated modes. Optical emission spectroscopy showed that the low-temperature growth of BP without plasma (Ar or phosphine) assistance using TMB is impossible. We conclude that there is a need to investigate other boron precursors for boron phosphide low-temperature growth to avoid carbon contamination in BP films.

Authentication of a product's originality by anticounterfeiting labels represents a crucial point toward protection against forgery. Fast and scalable fabrication methods of original labels with a high degree of protection are in high demand for the protection of valuable goods. Here, we propose a simple strategy for fabrication of hidden security tags with IR luminescent readout by the direct femtosecond laser patterning of silicon-erbium-silicon sandwiched thin films. The choice of laser processing parameters makes possible the creation of random or quasi-regular self-organized surface nanotextures. The controlled laser-driven oxidation accompanying this process provides simultaneous regulation of the film's optical properties and spontaneous emission yield of the embedded Er atoms. The regimes are detected when optically similar patterned areas demonstrate different Er emission intensities, allowing us to create hidden security tags with facile readout at the C-band telecommunication wavelengths. The obtained results take another step toward the application of IR-luminescent erbium-based anticounterfeiting labels for covert and/or forensic security levels.

We consider structure with single quantum well InP 5 nm thick grown by vapor phase epitaxy on n-GaP wafer. By classical capacitance-voltage profiling of Schottky diode on sample and electrochemical profiling, electron accumulation were detected in InP layer so existence of quantum well is confirmed. Results of admittance spectroscopy and deep-level transient spectroscopy showed defect formation in GaP layers above InP with energy position of Ec-0.21 eV, 0.30 eV и 0.93 eV.

The direct integration of epitaxial III-V and III-N heterostructures on Si substrates is a promising platform for the development of optoelectronic devices. Nanowires, due to their unique geometry, allow for the direct synthesis of semiconductor light-emitting diodes (LED) on crystalline lattice-mismatched Si wafers. Here, we present molecular beam epitaxy of regular arrays n-GaN/i-InGaN/p-GaN heterostructured nanowires and tripods on Si/SiO₂ substrates prepatterned with the use of cost-effective and rapid microsphere optical lithography. This approach provides the selective-area synthesis of the ordered nanowire arrays on large-area Si substrates. We experimentally show that the n-GaN NWs/n-Si interface demonstrates rectifying behavior and the fabricated n-GaN/i-InGaN/p-GaN NWs-based LEDs have electroluminescence in the broad spectral range, with a maximum near 500 nm, which can be employed for multicolor or white light screen development.

The influence of Ar gas additives on ≪black silicon≫ formation is shown in this work. The way to achieve the conical shape of Si texture using low Ar dilution is demonstrated. Also, a possibility of silicon nanowire width reduction keeping a high density of array is shown. No damage to the Si structure caused by Ar plasma was detected. The introduction of Ar into the plasma also does not affect electrical properties. The lifetime value after cryogenic etching with 5 sccm Ar flow remains at the same level of 0.7 ms. The resulting black silicon has a low total reflectance of 1 ± 0.5% in the range of 450–1000 nm in the overall 100 mm Si wafer surface.