AlGaN-based UV-B laser diode with a wavelength of 290 nm on 1 μm periodic concavo–convex pattern AlN on a sapphire substrate

Tanaka, Shunya; Teramura, Shohei; Shimokawa, Moe; Yamada, Kazuki; Omori, Tomoya; Iwayama, Sho; Sato, Kosuke; Miyake, Hideto; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu

doi:10.35848/1882-0786/abf763

Cited by 20 publications

(17 citation statements)

References 42 publications

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“…This gap has a distinct correlation with threading dislocation densities typical for AlGaN alloys, which were shown in Figure 1 of the review reported in [ 24 ]. This correlation reveals a very critical effect of threading dislocation density (TDD) on the threshold current density of DUV-LDs, which was further confirmed by direct measurements reported in [ 25 , 28 , 29 , 30 ], see Figure 2 a (TDD for the lowest threshold current density shown in this figure was not reported in [ 25 ], but we estimated TDD in the range of ~10 6 –10 7 cm −2 ). The efforts aimed at TDD reduction, thus improving the threshold current density, will be discussed in more detail in Section 2 .…”

Section: Introductionsupporting

confidence: 89%

“… ( a ) Experimental threshold current densities of UV laser diodes (symbols) fabricated by various approaches, including growth on concave-convex patterned AlN (PCCP AlN) vs. TDD [ 25 , 28 , 29 , 30 ]; the straight line approximates the data. ( b ) Measured internal quantum efficiency (symbols) of UV-LEDs emitting at various wavelengths as a function of TDD in the LED structure [ 31 , 32 , 33 ]; the solid line is the theoretical curve calculated by the model described in [ 34 ].…”

Section: Figurementioning

confidence: 99%

See 1 more Smart Citation

Towards Efficient Electrically-Driven Deep UVC Lasing: Challenges and Opportunities

Nikishin

Bernussi

Karpov³

2022

Nanomaterials

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The major issues confronting the performance of deep-UV (DUV) laser diodes (LDs) are reviewed along with the different approaches aimed at performance improvement. The impact of threading dislocations on the laser threshold current, limitations on heavy n- and p-doping in Al-rich AlGaN alloys, unavoidable electron leakage into the p-layers of (0001) LD structures, implementation of tunnel junctions, and non-uniform hole injection into multiple quantum wells in the active region are discussed. Special attention is paid to the current status of n- and p-type doping and threading dislocation density reduction, both being the factors largely determining the performance of DUV-LDs. It is shown that most of the above problems originate from intrinsic properties of the wide-bandgap AlGaN semiconductors, which emphasizes their fundamental role in the limitation of deep-UV LD performance. Among various remedies, novel promising technological and design approaches, such as high-temperature face-to-face annealing and distributed polarization doping, are discussed. Whenever possible, we provided a comparison between the growth capabilities of MOVPE and MBE techniques to fabricate DUV-LD structures.

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Section: Introductionsupporting

confidence: 89%

Section: Figurementioning

confidence: 99%

Towards Efficient Electrically-Driven Deep UVC Lasing: Challenges and Opportunities

Nikishin

Bernussi

Karpov³

2022

Nanomaterials

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“…It has also been reported that the density of micrometer‐sized V‐shaped pits and hillocks, which are formed on a wafer surface after device structure stacking, fabricated using the AlN nanopillar method was lower than that fabricated using the spontaneous nucleation method. [ 21,24 ] In addition, the energization tests conducted on a number of devices have clearly confirmed the higher yield of laser oscillation using the AlN nanopillar method. [ 21 ] Furthermore, it has been reported that hillock depends strongly on the threshold current in UV‐C LDs fabricated on AlN substrates, and this has a significant impact on device performance.…”

Section: Introductionmentioning

confidence: 96%

“…Thus, UV-B LDs have been fabricated on lattice-relaxed high-quality AlGaN template, in which a lattice-relaxing thickness film is stacked on the AlN underlayer and dislocations introduced during lattice relaxation are minimized by using the method. [17] Two methods of fabricating the AlGaN templates suitable at RT have been reported, namely, the spontaneous nucleation [20,22,23] and AlN nanopillar, [21,24] and the achievable dislocation density is slightly lower in the AlN nanopillar method. [21] Meanwhile, it is difficult to find a clear difference for the J th of LDs, specifically when only the top data are compared.…”

Section: Introductionmentioning

confidence: 99%

Performance of Ultraviolet‐B Laser Diodes on AlGaN Templates Prepared Using Different Fabrication Methods

Matsubara

Omori

Hasegawa

et al. 2023

Physica Status Solidi (a)

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Herein, the differences in the characteristics of ultraviolet‐B (UV‐B) laser diodes (LDs) are investigated and fabricated on AlGaN templates prepared using two types of fabrication methods: 1) spontaneous nucleation in which AlGaN is grown 3D from spontaneously generated AlN crystal nuclei and 2) AlN nanopillar in which AlGaN is grown on AlN nanopillars. The LD formed on the AlGaN fabricated using the AlN nanopillar method of slope efficiency and maximum peak light output power is improved four and six times, respectively, which are significantly better compared with the spontaneous nucleation method. The analysis also confirms the differences in injection efficiency and internal loss in the semiconductor crystal. Furthermore, detailed analysis of the current–voltage characteristics shows that the AlN nanopillar method has lower reverse leakage current and n‐value than the spontaneous nucleation method. Comparison of these differences with crystallographic properties suggests that these differences in device properties are manifested by differences in V‐shaped pits and dislocation density. The reduction of dislocations and V‐shaped pit density in an AlGaN template is important to realize high‐performance UV‐B LDs, and the AlN nanopillar method is found to be useful for the fabrication of a suitable AlGaN template.

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“…Here, a UV-B laser diode was fabricated through two breakthroughs: the use of relatively high-quality AlGaN with lattice relaxation [11,12] and the application of polarization doping [13,14] to the p-AlGaN cladding layer to achieve favorable optical cavity formation and high-current-density injection. To improve the performance of the fabricated UV-B laser diode, we have optimized the growth conditions of spontaneously nucleated AlN, [15] applied AlN nanopillars, [16,17] increased the optical confinement factor Γ, [18] and applied a refractive index waveguide structure. [19] Meanwhile, UV-B laser diodes use a combination of Cl 2 -inductively coupled plasma (ICP) dry etching and wet etching with the TMAH solution to form flat m-plane facets, [20] which are then used as mirrors.…”

mentioning

confidence: 99%

Development of High‐Reflectivity and Antireflection Dielectric Multilayer Mirrors for AlGaN‐Based Ultraviolet‐B Laser Diodes and their Device Applications

Yabutani

Hasegawa

Kondo

et al. 2023

Physica Status Solidi (a)

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Fabrication techniques for high‐reflectivity (HR) and antireflection (AR) dielectric multilayer mirrors for AlGaN‐based ultraviolet‐B (UV‐B) laser diodes are developed. After depositing several dielectric materials and evaluating their complex refractive indices via ellipsometry, it is determined that SiO2 as a low‐refractive‐index material and Ta2O5 as a high‐refractive‐index material are appropriate material combinations in the UV‐B region at a light wavelength of ≈300 nm due to their low extinction coefficients and large refractive index difference. Based on these results, HR mirror with a reflectance of >99% in the UV‐B region at a center wavelength of 310 nm and an AR mirror with a reflectance of ≈8% in the same wavelength range are demonstrated; a mirror with reflectance that is almost equal to the designed value is demonstrated. Furthermore, these mirrors are coated on the respective edge surfaces of the UV‐B laser diodes. A comparison of the characteristics of the same device before and after edge coating reveals a reduction in the threshold current density of laser oscillation, whereas, simultaneously, an increase in slope efficiency and external differential quantum efficiency is observed. The improvement of these device characteristics, estimated from the above reflectance values, is confirmed to be almost theoretically explainable.

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AlGaN-based UV-B laser diode with a wavelength of 290 nm on 1 μm periodic concavo–convex pattern AlN on a sapphire substrate

Cited by 20 publications

References 42 publications

Towards Efficient Electrically-Driven Deep UVC Lasing: Challenges and Opportunities

Towards Efficient Electrically-Driven Deep UVC Lasing: Challenges and Opportunities

Performance of Ultraviolet‐B Laser Diodes on AlGaN Templates Prepared Using Different Fabrication Methods

Development of High‐Reflectivity and Antireflection Dielectric Multilayer Mirrors for AlGaN‐Based Ultraviolet‐B Laser Diodes and their Device Applications

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