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1. Impact of a prestrained graded InGaN/GaN interlayer towards enhanced optical characteristics of a multi-quantum well LED based on silicon substrate

   https://doi.org/10.1364/AO.470083  

   Das, Samadrita; Lenka, Trupti_Ranjan; Talukdar, Fazal_Ahmed; Sadaf, Sharif_Md; Velpula, Ravi_Teja; Nguyen, Hieu_Pham_Trung (October 2022, Applied Optics)

   This paper presents alternate pairs of InGaN/GaN prestrained layers with varying indium compositions, which are inserted between the GaN/InGaN MQW active region and the n-GaN layer in a light-emitting diode (LED) nanostructure in order to obtain enhanced optical characteristics. The device is mounted on a silicon substrate followed by a GaN buffer layer that promotes charge injection by minimizing the energy barrier between the electrode and active layers. The designed device attains more than 2.897% enhancement in efficiency when compared with the conventional LED, which is attributed to the reduction of a polarization field within the MQW region. The proposed device with 15% indium composition in the prestrained layer attains a maximum efficiency of 85.21% and a minimized efficiency droop of 3.848% at an injection current of 40 mA, with high luminous power in the output spectral range. The device also shows a minimum blueshift in the spectral range, indicating a decrease in the piezoelectric polarization. 

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2. Oxygen Incorporation in the Molecular Beam Epitaxy Growth of Sc _x Ga _1−x N and Sc _x Al _1−x N

   https://doi.org/10.1002/pssb.201900612  

   Casamento, Joseph; Xing, Huili Grace; Jena, Debdeep (January 2020, physica status solidi (b))

   Secondary‐ion mass spectrometry (SIMS) is used to determine impurity concentrations of carbon and oxygen in two scandium‐containing nitride semiconductor multilayer heterostructures: Sc_xGa_1−xN/GaN and Sc_xAl_1−xN/AlN grown by molecular beam epitaxy (MBE). In the Sc_xGa_1−xN/GaN heterostructure grown in metal‐rich conditions on GaN–SiC template substrates with Sc contents up to 28 at%, the oxygen concentration is found to be below 1 × 10¹⁹ cm⁻³, with an increase directly correlated with the scandium content. In the Sc_xAl_1−xN–AlN heterostructure grown in nitrogen‐rich conditions on AlN–Al₂O₃template substrates with Sc contents up to 26 at%, the oxygen concentration is found to be between 10¹⁹and 10²¹ cm⁻³, again directly correlated with the Sc content. The increase in oxygen and carbon takes place during the deposition of scandium‐alloyed layers. 

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3. Epitaxial Sc _x Al _{1− x} N on GaN exhibits attractive high-K dielectric properties

   https://doi.org/10.1063/5.0075636  

   Casamento, Joseph; Lee, Hyunjea; Maeda, Takuya; Gund, Ved; Nomoto, Kazuki; van Deurzen, Len; Turner, Wesley; Fay, Patrick; Mu, Sai; Van de Walle, Chris G.; et al (April 2022, Applied Physics Letters)

   Epitaxial Sc_xAl_1−xN thin films of ∼100 nm thickness grown on metal polar GaN substrates are found to exhibit significantly enhanced relative dielectric permittivity (ε_r) values relative to AlN. ε_rvalues of ∼17–21 for Sc mole fractions of 17%–25% ( x = 0.17–0.25) measured electrically by capacitance–voltage measurements indicate that Sc_xAl_1−xN has the largest relative dielectric permittivity of any existing nitride material. Since epitaxial Sc_xAl_1−xN layers deposited on GaN also exhibit large polarization discontinuity, the heterojunction can exploit the in situ high-K dielectric property to extend transistor operation for power electronics and high-speed microwave applications. 

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4. Improved Performance of Electron Blocking Layer Free AlGaN Deep Ultraviolet Light-Emitting Diodes Using Graded Staircase Barriers

   https://doi.org/10.3390/mi12030334  

   Jain, Barsha; Velpula, Ravi Teja; Patel, Moulik; Sadaf, Sharif Md.; Nguyen, Hieu Pham (March 2021, Micromachines)

   null (Ed.)

   To prevent electron leakage in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs), Al-rich p-type AlxGa(1−x)N electron blocking layer (EBL) has been utilized. However, the conventional EBL can mitigate the electron overflow only up to some extent and adversely, holes are depleted in the EBL due to the formation of positive sheet polarization charges at the heterointerface of the last quantum barrier (QB)/EBL. Subsequently, the hole injection efficiency of the LED is severely limited. In this regard, we propose an EBL-free AlGaN deep UV LED structure using graded staircase quantum barriers (GSQBs) instead of conventional QBs without affecting the hole injection efficiency. The reported structure exhibits significantly reduced thermal velocity and mean free path of electrons in the active region, thus greatly confines the electrons over there and tremendously decreases the electron leakage into the p-region. Moreover, such specially designed QBs reduce the quantum-confined Stark effect in the active region, thereby improves the electron and hole wavefunctions overlap. As a result, both the internal quantum efficiency and output power of the GSQB structure are ~2.13 times higher than the conventional structure at 60 mA. Importantly, our proposed structure exhibits only ~20.68% efficiency droop during 0–60 mA injection current, which is significantly lower compared to the regular structure. 

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5. Effects of polarized-induced doping and graded composition in an advanced multiple quantum well InGaN/GaN UV-LED for enhanced light technology

   https://doi.org/10.1088/2631-8695/ac4fb1  

   Das, Samadrita; Lenka, Trupti Ranjan; Talukdar, Fazal Ahmed; Velpula, Ravi Teja; Jain, Barsha; Nguyen, Hieu Pham; Crupi, Giovanni (March 2022, Engineering Research Express)

   Abstract In this paper, a light-emitting diode in the ultra-violet range (UV-LED) with multiple-quantum wells (MQWs) of InGaN/GaN is designed and analyzed through Technology Computer-Aided Design (TCAD) simulations. The polarization effects in III-nitride heterojunction and the effects of graded composition in the electron blocking layer (EBL) are exploited to enhance the performance of the proposed UV-LED. It is observed that the effect of graded composition in the EBL helps to enhance the electrical and optical performance of the LED, thereby enabling the achievement of some promising results. The simulation-based results demonstrated that superior internal efficiency and an inferior leakage current are achieved by using a graded Al composition in the EBL rather than a uniform composition. The reported results also confirm the remarkable improvement of the light output power by 17% at ∼100 mA when using the graded composition and also show a reduction in series resistance leading to more current. Graded Al composition in the EBL results in the enhancement of electroluminescence spectra (i.e., an increase in the peak of the spectral density). 

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