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i l St. Petersburg Polytechnic University Journal. Physics and Mathematics. 2022 Vol. 15, No. 3.3 Научно-технические ведомости СПбГПУ. Физико-математические науки. 15 (3.3) 2022
Conference materials UDC 621.373.826
DOI: https://doi.org/10.18721/JPM.153.346
The effect of mesa-stripe design parameters on the 975 nm laser diode output characteristics
A. V. Fomin \ E. M. Filonenko 1H, S. A. Kryukov \ S. Kh. Nazhmetov 1 1 FSUE "RFNC-VNIITF named after Academ. E. I. Zababakhin", Snezhinsk, Russia
H dep5@vniitf.ru
Abstract. The present work is devoted to evaluating the effect of mesa-stripe design parameters on the output characteristics of 975 nm InGaAs/GaAs/AlGaAs laser diodes with the emitting stripe width W = 100 ^m and the cavity length L = 4 mm. The output power, threshold current, central wavelength, and full spectral width at half maximum values were analyzed when comparing the two variants of mesa-stripe design to determine the optimal etching depth of semiconductor structure. Two variants of the mesa-stripe design were obtained by plasma-chemical etching to different depths of the heterostructure. According to the results of the study for the mesa-stripe design formed by etching to the p-cladding layer of the laser heterostructure, a less scatter of the controlled parameters within a group of fabricated laser diodes and effective suppression of parasitic lateral modes in the LD cavity were revealed.
Keywords: optoelectronics, laser diode, optical confinement, mesa-stripe design, etching depth, electrooptical parameters
Citation: Fomin A. V., Filonenko E. M., Kryukov S. A., Nazhmetov S. Kh., The effect of mesa-stripe design parameters on the 975 nm laser diode output characteristics. St. Petersburg State Polytechnical University Journal. Physics and Mathematics, 15 (3.3) (2022) 235—238. DOI: https://doi.org/10.18721/JPM.153.346
This is an open access article under the CC BY-NC 4.0 license (https://creativecommons. org/licenses/by-nc/4.0/)
Материалы конференции УДК 621.373.826
DOI: https://doi.org/10.18721/JPM.153.346
Исследование влияния параметров мезаполосковой конструкции лазерных диодов спектрального диапазона 975 нм на характеристики излучения
А. В. Фомин 1, Е. М. Филоненко 1Н, С. А. Крюков 1, С. Х. Нажметов 1 1 ФГУП «РФЯЦ-ВНИИТФ им. академ. Е.И. Забабахина» , Снежинск, Россия
н dep5@vniitf.ru
Аннотация. В настоящей работе приведены результаты оценки влияния конструкции чипа на выходные характеристики лазерных диодов InGaAs/GaAs/ AlGaAs спектрального диапазона 975 нм с шириной полоска W = 100 мкм и длиной резонатора L = 4 мм. При сравнении двух вариантов мезаполосковой конструкции анализировались значения выходной мощности, порогового тока, центральной длины волны и ширины спектра на полувысоте с целью определения оптимальной глубины травления полупроводниковой гетероструктуры. Два варианта мезаполосковой конструкции были получены плазмохимическим травлением канавок на разную глубину гетеророструктуры. По результатам исследования для конструкции мезаполоска, образованного травлением до слоя p-эмиттера лазерной гетероструктуры, был выявлен меньший разброс контролируемых параметров внутри группы изготовленных лазерных диодов и продемонстрировано эффективное подавление паразитных латеральных мод в резонаторе ЛД.
© Fomin A. V., Filonenko E. M., Kryukov S. A., Nazhmetov S. Kh., 2022. Published by Peter the Great St.Petersburg Polytechnic University.
^St. Petersburg Polytechnic University Journal. Physics and Mathematics. 2022 Vol. 15, No. 3.3
Ключевые слова: оптоэлектроника, лазерный диод, оптическое ограничение, мезаполосковая конструкция, глубина травления, электрооптические характеристики
Ссылка при цитировании: Фомин А. В., Филоненко Е. М., Крюков С. А., Нажметов С. Х. Исследование влияния параметров мезаполосковой конструкции лазерных диодов спектрального диапазона 975 нм на характеристики излучения // Научно-технические ведомости СПбГПУ. Физико-математические науки. 2022. Т. 15. № 3.3. C. 235—238. DOI: https://doi.org/10.18721/JPM.153.346
Статья открытого доступа, распространяемая по лицензии CC BY-NC 4.0 (https:// creativecommons.org/licenses/by-nc/4.0/)
Introduction
Today, high-power laser diodes (LDs) emitting at 975 nm are widely used for fiber laser pumping [1, 2]. In the LD design, a stimulated emission is generated in quantum well region between waveguide layers which, in turn, are surrounded by claddings. The plane-parallel Fabry-Perot cavity is formed by two cleaved facets of semiconductor crystal [3]. Optical confinement of LD radiation in the vertical direction is formed directly during epitaxial growth of laser heterostructure waveguide layers, while the formation of a waveguide necessary to create a lateral direction of LD radiation is considered to be a crucial design problem to be solved in the course of post-stage operations of high-power LD technology along with the development of optical and contact coatings.
Lateral confinement of radiation in a laser heterostructure can be attained by creating an effective refractive-index step, Aneff) at the boundary with radiation region or be achieved due to a difference in gain in this direction [3, 4]. An appropriate LD design in the first case can be formed by etching the heterostructure down to the n-type cladding, the walls of the etching profile optically constraining the radiation in the lateral direction (Fig. 1, a). A gain step, Ag, can be similarly achieved by forming an LD mesa-stripe by etching the heterostructure, yet with the etch front reaching only the p-type cladding (Fig. 2, b). In this case, the concentration of charge carriers is sufficiently high only in a limited region under the stripe creating conditions to overcome optical loss [3, 4].
This work was aimed at considering the above-mentioned design solutions and was devoted to evaluating the effect of the etching depth of the grooves forming the mesa-stripe on the output parameters of the LDs emitting at 975 nm in order to determine the optimal mesa-stripe geometry for the existing design of InGaAs/GaAs/AlGaAs laser heterostructure.
a)
Grooves
b)
Grooves
p-side
□-side
Q\V
p-side u г * -ow- и
n-side
Fig. 1. Mesa-stripe designs with etching to the n-type cladding (a) and etching to the p-type cladding (b)
Materials and Methods
The InGaAs/GaAs/AlGaAs heterostructure samples to be studied were grown by metalorganic chemical vapour deposition (MOCVD) method. The topology of the produced LDs was a mesa-stripe design with different depths of etched grooves defining mesas, denoted further as deep and shallow ones. In the first case, the etch front reached the n-cladding region. In the second case, the etch front reached the p-cladding without affecting the laser heterostructure waveguide and the active region. The etching depth was controlled by profilometry and SEM analysis. In the course of this work, laser diodes of two types of mesa-stripe designs were fabricated having the emitting stripe width W = 100 ^m and the cavity length L = 4 mm. For output characteristics measurements the LDs with different mesa-stripe designs were mounted on heatsinks with thin-film AuSn solder [5].
© Фомин А. В., Филоненко Е. М., Крюков С. А., Нажметов С. Х., 2022. Издатель: Санкт-Петербургский политехнический университет Петра Великого.
Physical optics
Results and discussion
The output characteristics of two groups of LDs without applied cavity mirrors and with different mesa design depths for QCW generation mode of up to a current of 3 A are shown in Fig. 2. Table 1 shows the average values of wavelength, 1, full width at half maximum, FWHM, output power, P, threshold current, Ith, and estimated scatter of parameters for each LD group. A greater scatter of spectral characteristics and of output power values is observed within the group of deep mesa LDs, while the scatter of threshold current values is identical for both groups (Fig. 2, a, b). Thus, the manufactured shallow mesa LD design is characterized by more stable values obtained for the controlled parameters.
Table 1
Average values of controlled parameters and scatter estimation for two groups of LDs with different mesa-stripe designs
Design Number of LDs Average value Standard deviation
X, nm FWHM, nm Ith, A P, W X, nm FWHM, nm Ith, A P, W
Deep mesa 43 974.3 3.3 0.34 1.2 0.5 0.6 0.02 0.1
Shallow mesa 43 975.1 3.1 0.34 1.2 0.2 0.2 0.01 0.0
Fig. 2. Correlation plots of FWHM and central wavelength 1 (a) and LDs output power and threshold current for two groups of LDs with shallow and deep mesas (b)
The output characteristics were also measured in the CW mode for LDs with applied mirrors (Fig. 3). The typical value of the external differential efficiency for deep mesa LDs was n = 0.95 W/A, that for shallow mesa LDs being n = 1.05 W/A. Typical values of FWHM for deep mesa LDs can reach 10 nm at the current of 12 A provided that several local maxima are present in the spectrum (Fig. 3, a). At the same time, typical values of FWHM for shallow mesa LDs made up 3.7—5 nm at the current of 12 A (Fig. 3, b).
i..mn mn
Fig. 3. Typical spectra for LDs with mirrors obtained in CW mode at 12 A current: deep (a) and
shallow mesa-stripe designs (b)
St. Petersburg Polytechnic University Journal. Physics and Mathematics. 2022 Vol. 15, No. 3.3
Conclusion
The studies of the output characteristics for two groups of LDs allowed establishing the advantage of the shallow mesa design, which is characterized by obtaining more reproducible values of the controlled LD parameters. Lower values of differential efficiency, as well as the presence of several local maxima in the spectrum of deep mesa-stripe LDs may indicate the formation of conditions suitable for amplification of higher order modes in this type of design. In turn, the shallow mesa design allows effectively suppressing the parasitic lateral modes in the resonator, as evidenced by the presence of a single local maximum in the LD spectrum.
1. Duesterberg R., Xu L., Skidmore J. A., Guo J., Cheng J., Du J., Zucker E. P., 100W high-brightness multi-emitter laser pump. High-Power Diode Laser Technology and Applications IX, edited by Mark S. Zediker, Proc. of SPIE. 7918 (2011) 79180V.
2. Skidmore J., Peters M., Rossin V., Guo J., Xiao Y., Cheng J., Zucker E., Advances in high-power 9XXnm laser diodes for pumping fiber lasers. High-Power Diode Laser Technology and Applications XIV, edited by Mark S. Zediker, Proc. of SPIE. 9733 (2016) 97330B.
3. Zhukov А. Е., Lasers based on semiconductor nanostructures [in Russian], Elmor, Saint-Petersburg, 2007.
4. Diehl R., High-Power Diode Lasers: Fundamentals, Technology, Applications with Con-tributions by Numerous Experts, Applied Physics. 78 (2000).
5. Filonenko E. M., Fomin A. V., Ivanov V. V., Features ofAu(80)Sn(20) thin film solder manufacturing technology, IOP Conference Series: Materials Science and Engineering. 781 (2020) 012019.
REFERENCES
THE AUTHORS
FILONENKO Elena M.
dep5@vniitf.ru
ORCID: 0000-0002-9477-612X
KRYUKOV Sergey A. dep5@vniitf.ru
FOMIN Alexey V. dep5@vniitf.ru
NAZHMETOV Salavat Kh.
dep5@vniitf.ru
Received 24.07.2022. Approved after reviewing 25.07.2022. Accepted 25.07.2022.
© Peter the Great St. Petersburg Polytechnic University, 2022
