which are environmentally friendly and enable portability and high efficiency. Up to date, great progress has been made on the UVC light-emitting diodes (LEDs) by using active regions of AlGaN multiple quantum wells (MQWs) .[8-14] However, the optical output power of current UVC LEDs drops significantly as the light emission wavelength gets shorter. Those LEDs suffer from poor hole injection efficiency in high-Al-content p-type AlGaN, low internal quantum efficiency (IQE) caused by large-lattice-mismatch heteroepitaxy, and strong quantum-confined Stark effect (QCSE), as well as the absorption by the nontransparent GaN contact layers. [15][16][17] A promising approach that dramatically improves the light output power is electron-beam (e-beam) pumping, especially for the short-wavelength UVC spectral range. [3,[18][19][20][21][22][23][24] This approach allows one to bypass the need for p-type or n-type injection layers and, thus, can largely increase the carrier injection efficiency. This provides a unique advantage over conventional LEDs at UVC range, since the p-type doping for high-Al-content AlGaN is High-output-power electron-beam (e-beam) pumped deep ultraviolet (DUV) light sources, operating at 230-270 nm, are achieved by adjusting the well thickness of binary ultrathin GaN/AlN multiple quantum wells. These structures are fabricated on high-quality thermally annealed AlN templates by metal-organic chemical vapor deposition. Owing to the reduced dislocation density, large electron-hole overlap, and efficient carrier injection by e-beam, the DUV light sources demonstrate high output powers of 24.8, 122.5, and 178.8 mW at central wavelengths of 232, 244, and 267 nm, respectively. Further growth optimization and employing an e-gun with increased beam current lead to a record output power of ≈2.2 W at emission wavelength of ≈260 nm, the key wavelength for water sterilization. This work manifests the practical levels of high-output-power DUV light sources operated by using e-beam pumping method. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adom.201801763.Solid-state deep ultraviolet (DUV) optoelectronic devices in the spectral range of 200-280 nm, i.e., ultraviolet-C (UVC), have attracted much attention for their wide applications in sterilization, medical treatment, security, solar-blind photodetection, and so on. [1][2][3][4][5][6][7] Currently, Al(Ga)N material system is the most promising candidate for solid-state UVC light sources

Monolayer (ML)-scale GaN/AlN multiple quantum well (MQW) structures for electron-beam-pumped ultraviolet (UV) emitters are grown on c-sapphire substrates by using plasma-assisted molecular beam epitaxy under controllable metal-rich conditions, which provides the spiral growth of densely packed atomically smooth hillocks without metal droplets. These structures have ML-stepped terrace-like surface topology in the entire QW thickness range from 0.75–7 ML and absence of stress at the well thickness below 2 ML. Satisfactory quantum confinement and mitigating the quantum-confined Stark effect in the stress-free MQW structures enable one to achieve the relatively bright UV cathodoluminescence with a narrow-line (~15 nm) in the sub-250-nm spectral range. The structures with many QWs (up to 400) exhibit the output optical power of ~1 W at 240 nm, when pumped by a standard thermionic-cathode (LaB6) electron gun at an electron energy of 20 keV and a current of 65 mA. This power is increased up to 11.8 W at an average excitation energy of 5 µJ per pulse, generated by the electron gun with a ferroelectric plasma cathode at an electron-beam energy of 12.5 keV and a current of 450 mA.

Spreading resistance microscopy (SRM) was used to study nanoscale variations in electronic and structural properties of an ultrathin near-surface GaN/AlN quantum well (QW). In the SRM images of the growth surface of the GaN/AlN QW heterostructure, an inhomogeneous current contrast was detected in the form of disk-like regions of increased conductivity with the sizes in the range of 50–160 nm and a density of ∼1.7 × 109 cm−2. Analysis of the current contrast dependence on the polarity of the sample dc bias and the growth surface morphology revealed that these regions are the GaN islands of various thicknesses. These islands spread predominantly within the crystal grains rather than along their boundaries and represent electron localization sites in the QW plane. The results demonstrate the applicability of SRM as an express and non-destructive technique to delineate quantitatively in-plane fluctuations in the electronic and structural properties of near-surface GaN/AlN QWs with a high spatial resolution of ∼10 nm.

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Photoconductive atomic force microscopy (PC-AFM) allows one to study the influence of illumination on the conductive properties of different samples at the nanoscale. However, for such measurements to be considered reliable, one has to be sure that illumination does not impact the tip–sample contact force. The change of the contact force may be caused by the influence of radiation on the atomic force microscope's position sensitive detector (PSD) as well as the probe and sample. There are certain approaches to reduce this illumination influence; however, they cannot always be implemented. Therefore, it is important to perform a detailed study of the influence of illumination on the PSD, the probe, and the sample during measurements in the PC-AFM mode. In this paper, this was done by studying the mechanism by which elevation is formed in topographic images of the cleaved GaAs substrate surface under lateral continuous wave (CW) laser illumination, with λ = 1064 and 404 nm. It was demonstrated that the illumination results, mainly, in the thermal expansion of the tip and the sample, as well as the generation of a thermal stress in the cantilever. The authors consider the cases in which these effects can increase the tip–sample contact force during PC-AFM measurements and suggest simple approaches by which the increase in force can be minimized. Also, the authors developed the model of thermal expansion of the GaAs sample fixed in the holder under CW laser illumination. Based on this model, the approach was suggested for estimation of the thermal contact conductance value for different solid–solid interfaces.