Editorial

3 pages, 176 KiB

Open AccessEditorial

Special Issue: Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices)

by Valentin Jmerik

Nanomaterials 2022, 12(10), 1685; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12101685 - 15 May 2022

Cited by 2 | Viewed by 1199

Semiconductor heterostructures form the basis of modern electronics and optoelectronics, and the study of physical phenomena in them, along with the development of technological methods for their manufacture, is actively carried out all over the world to ensure progress in the output parameters [...] Read more.

Semiconductor heterostructures form the basis of modern electronics and optoelectronics, and the study of physical phenomena in them, along with the development of technological methods for their manufacture, is actively carried out all over the world to ensure progress in the output parameters of devices [...] Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

Research

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16 pages, 5974 KiB

Open AccessEditor’s ChoiceArticle

Monolayer-Scale GaN/AlN Multiple Quantum Wells for High Power e-Beam Pumped UV-Emitters in the 240–270 nm Spectral Range

by Valentin Jmerik, Dmitrii Nechaev, Kseniya Orekhova, Nikita Prasolov, Vladimir Kozlovsky, Dmitry Sviridov, Mikhail Zverev, Nikita Gamov, Lars Grieger, Yixin Wang, Tao Wang, Xinqiang Wang and Sergey Ivanov

Nanomaterials 2021, 11(10), 2553; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11102553 - 29 Sep 2021

Cited by 10 | Viewed by 2562

Abstract

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. [...] Read more.

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. Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

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9 pages, 1925 KiB

Open AccessArticle

High Hole Concentration and Diffusion Suppression of Heavily Mg-Doped p-GaN for Application in Enhanced-Mode GaN HEMT

by Jin-Ji Dai, Thi Thu Mai, Ssu-Kuan Wu, Jing-Rong Peng, Cheng-Wei Liu, Hua-Chiang Wen, Wu-Ching Chou, Han-Chieh Ho and Wei-Fan Wang

Nanomaterials 2021, 11(7), 1766; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11071766 - 07 Jul 2021

Cited by 8 | Viewed by 3987

Abstract

The effect of Mg doping on the electrical and optical properties of the p-GaN/AlGaN structures on a Si substrate grown by metal organic chemical vapor deposition was investigated. The Hall measurement showed that the activation efficiency of the sample with a 450 sccm [...] Read more.

The effect of Mg doping on the electrical and optical properties of the p-GaN/AlGaN structures on a Si substrate grown by metal organic chemical vapor deposition was investigated. The Hall measurement showed that the activation efficiency of the sample with a 450 sccm Cp₂Mg flow rate reached a maximum value of 2.22%. No reversion of the hole concentration was observed due to the existence of stress in the designed sample structures. This is attributed to the higher Mg-to-Ga incorporation rate resulting from the restriction of self-compensation under compressive strain. In addition, by using an AlN interlayer (IL) at the interface of p-GaN/AlGaN, the activation rate can be further improved after the doping concentration reaches saturation, and the diffusion of Mg atoms can also be effectively suppressed. A high hole concentration of about 1.3 × 10¹⁸ cm⁻³ can be achieved in the p-GaN/AlN-IL/AlGaN structure. Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

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8 pages, 2263 KiB

Open AccessArticle

Wet-Etched Microlens Array for 200 nm Spatial Isolation of Epitaxial Single QDs and 80 nm Broadband Enhancement of Their Quantum Light Extraction

by Shulun Li, Xiangjun Shang, Yao Chen, Xiangbin Su, Huiming Hao, Hanqing Liu, Yu Zhang, Haiqiao Ni and Zhichuan Niu

Nanomaterials 2021, 11(5), 1136; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11051136 - 27 Apr 2021

Cited by 7 | Viewed by 2109

Abstract

Uniform arrays of three shapes (

g a u s s

,

h a t

, and

p e a k

) of GaAs microlenses (MLs) by wet-etching are demonstrated, ∼200 nm spatial isolation of epitaxial single QDs embedded (

λ

: 890–990 [...] Read more.

Uniform arrays of three shapes (

g a u s s

,

h a t

, and

p e a k

) of GaAs microlenses (MLs) by wet-etching are demonstrated, ∼200 nm spatial isolation of epitaxial single QDs embedded (

λ

: 890–990 nm) and broadband (

Δ λ \sim 80

nm) enhancement of their quantum light extraction are obtained, which is also suitable for telecom-band epitaxial QDs. Combined with the bottom distributed Bragg reflector, the

h a t

-shaped ML forms a cavity and achieves the best enhancement: extraction efficiency of 26%, Purcell factor of 2 and single-photon count rate of

7 \times 10^{6}

counts per second at the first lens; while the

g a u s s

-shaped ML shows a broader band (e.g., longer

λ

) enhancement. In the MLs, single QDs with featured exciton emissions are observed, whose time correlations prove single-photon emission with multi-photon probability

g^{(2)} (0) = 0.02

; some QDs show both biexciton

X X

and exciton X emissions and exhibit a perfect cascade feature. This work could pave a step towards a scalable array of QD single-photon sources and the application of QD photon-pair emission for entanglement experiments. Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

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14 pages, 21867 KiB

Open AccessArticle

One-Stage Formation of Two-Dimensional Photonic Crystal and Spatially Ordered Arrays of Self-Assembled Ge(Si) Nanoislandson Pit-Patterned Silicon-On-Insulator Substrate

by Alexey V. Novikov, Zhanna V. Smagina, Margarita V. Stepikhova, Vladimir A. Zinovyev, Sergey A. Rudin, Sergey A. Dyakov, Ekaterina E. Rodyakina, Alexey V. Nenashev, Sergey M. Sergeev, Artem V. Peretokin and Anatoly V. Dvurechenskii

Nanomaterials 2021, 11(4), 909; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11040909 - 02 Apr 2021

Cited by 10 | Viewed by 1890

Abstract

A new approach to improve the light-emitting efficiency of Ge(Si) quantum dots (QDs) by the formation of an ordered array of QDs on a pit-patterned silicon-on-insulator (SOI) substrate is presented. This approach makes it possible to use the same pre-patterned substrate both for [...] Read more.

A new approach to improve the light-emitting efficiency of Ge(Si) quantum dots (QDs) by the formation of an ordered array of QDs on a pit-patterned silicon-on-insulator (SOI) substrate is presented. This approach makes it possible to use the same pre-patterned substrate both for the growth of spatially ordered QDs and for the formation of photonic crystal (PhC) in which QDs are embedded. The periodic array of deep pits on the SOI substrate simultaneously serves as a template for spatially ordering of QDs and the basis for two-dimensional PhCs. As a result of theoretical and experimental studies, the main regularities of the QD nucleation on the pre-patterned surface with deep pits were revealed. The parameters of the pit-patterned substrate (the period of the location of the pits, the pit shape, and depth) providing a significant increase of the QD luminescence intensity due to the effective interaction of QD emission with the PhC modes are found. Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

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8 pages, 1829 KiB

Open AccessEditor’s ChoiceArticle

Correlation between Optical Localization-State and Electrical Deep-Level State in In_0.52Al_0.48As/In_0.53Ga_0.47As Quantum Well Structure

by Il-Ho Ahn, Deuk Young Kim and Sejoon Lee

Nanomaterials 2021, 11(3), 585; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11030585 - 26 Feb 2021

Cited by 3 | Viewed by 1765

Abstract

The peculiar correlationship between the optical localization-state and the electrical deep-level defect-state was observed in the In_0.52Al_0.48As/In_0.53Ga_0.47As quantum well structure that comprises two quantum-confined electron-states and two hole-subbands. The sample clearly exhibited the Fermi edge [...] Read more.

The peculiar correlationship between the optical localization-state and the electrical deep-level defect-state was observed in the In_0.52Al_0.48As/In_0.53Ga_0.47As quantum well structure that comprises two quantum-confined electron-states and two hole-subbands. The sample clearly exhibited the Fermi edge singularity (FES) peak in its photoluminescence spectrum at 10–300 K; and the FES peak was analyzed in terms of the phenomenological line shape model with key physical parameters such as the Fermi energy, the hole localization energy, and the band-to-band transition amplitude. Through the comprehensive studies on both the theoretical calculation and the experimental evaluation of the energy band profile, we found out that the localized state, which is separated above by ~0.07 eV from the first excited hole-subband, corresponds to the deep-level state, residing at the position of ~0.75 eV far below the conduction band (i.e., near the valence band edge). Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

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14 pages, 11139 KiB

Open AccessArticle

Fractional Charge States in the Magneto-Photoluminescence Spectra of Single-Electron InP/GaInP₂ Quantum Dots

by Alexander Mintairov, Dmitrii Lebedev, Alexei Vlasov, Andrey Bogdanov, Shahab Ramezanpour and Steven Blundell

Nanomaterials 2021, 11(2), 493; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11020493 - 16 Feb 2021

Cited by 4 | Viewed by 1899

Abstract

We used photoluminescence spectra of single electron quasi-two-dimensional InP/GaInP₂ islands having Wigner-Seitz radius ~4 to measure the magnetic-field dispersion of the lowest s, p, and d single-particle states in the range 0–10 T. The measured dispersion revealed up to a [...] Read more.

We used photoluminescence spectra of single electron quasi-two-dimensional InP/GaInP₂ islands having Wigner-Seitz radius ~4 to measure the magnetic-field dispersion of the lowest s, p, and d single-particle states in the range 0–10 T. The measured dispersion revealed up to a nine-fold reduction of the cyclotron frequency, indicating the formation of nano-superconducting anyon or magneto-electron (e_m) states, in which the corresponding number of magnetic-flux-quanta vortexes and fractional charge were self-generated. We observed a linear increase in the number of vortexes versus the island size, which corresponded to a critical vortex radius equal to the Bohr radius and closed-packed topological vortex arrangements. Our observation explains the microscopic mechanism of vortex attachment in composite fermion theory of the fractional quantum Hall effect, allows its description in terms of self-localization of e_ms and represents progress towards the goal of engineering anyon properties for fault-tolerant topological quantum gates. Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

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21 pages, 5924 KiB

Open AccessEditor’s ChoiceArticle

Phonons in Short-Period GaN/AlN Superlattices: Group-Theoretical Analysis, Ab initio Calculations, and Raman Spectra

by Valery Davydov, Evgenii Roginskii, Yuri Kitaev, Alexander Smirnov, Ilya Eliseyev, Dmitrii Nechaev, Valentin Jmerik and Mikhail Smirnov

Nanomaterials 2021, 11(2), 286; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11020286 - 22 Jan 2021

Cited by 16 | Viewed by 2282

Abstract

We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using [...] Read more.

We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using detailed group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals is established. Ab initio calculations in the framework of the density functional theory, aimed at studying the phonon states, are performed for SLs with both equal and unequal layer thicknesses. The frequencies of the vibrational modes are calculated, and atomic displacement patterns are obtained. Raman spectra are calculated and compared with the experimental ones. The results of the ab initio calculations are in good agreement with the experimental Raman spectra and the results of the group-theoretical analysis. As a result of comprehensive studies, the correlations between the parameters of acoustic and optical phonons and the structure of SLs are obtained. This opens up new possibilities for the analysis of the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy. The results obtained can be used to optimize the growth technologies aimed to form structurally perfect short-period GaN/AlN SLs. Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

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15 pages, 3965 KiB

Open AccessArticle

Surface Nanostructuring during Selective Area Epitaxy of Heterostructures with InGaAs QWs in the Ultra-Wide Windows

by Viktor Shamakhov, Dmitriy Nikolaev, Sergey Slipchenko, Evgenii Fomin, Alexander Smirnov, Ilya Eliseyev, Nikita Pikhtin and Peter Kop`ev

Nanomaterials 2021, 11(1), 11; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11010011 - 23 Dec 2020

Cited by 8 | Viewed by 1943

Abstract

Selective area epitaxy (SAE) is widely used in photonic integrated circuits, but there is little information on the use of this technique for the growth of heterostructures in ultra-wide windows. Samples of heterostructures with InGaAs quantum wells (QWs) on GaAs (100) substrates with [...] Read more.

Selective area epitaxy (SAE) is widely used in photonic integrated circuits, but there is little information on the use of this technique for the growth of heterostructures in ultra-wide windows. Samples of heterostructures with InGaAs quantum wells (QWs) on GaAs (100) substrates with a pattern of alternating stripes (100-μm-wide SiO₂ mask/100-μm-wide window) were grown using metalorganic chemical vapour deposition (MOCVD). It was found that due to a local change in the growth rate of InGaAs QW in the window, the photoluminescence (PL) spectra measured from the edge to the center of the window exhibited maximum blueshifts of 14 and 19 meV at temperatures of 80 K and 300 K, respectively. Using atomic force microscopy, we have demonstrated that the surface morphologies of structures grown using standard epitaxy or SAE under identical MOCVD growth conditions correspond to a step flow growth with a step height of ~1.5 ML or a step bunching growth mode, respectively. In the structures grown with the use of SAE, a strong variation in the surface morphology in an ultra-wide window from its center to the edge was revealed, which is explained by a change in the local misorientation of the layer due to a local change in the growth rate over the width of the window. Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

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