ИССЛЕДОВАНИЕ ВОЗМОЖНОСТЕЙ УЛУЧШЕНИЯЭНЕРГОМАССОВЫХ ХАРАКТЕРИСТИК СОЛНЕЧНЫХ ЭЛЕМЕНТОВ С ИСПОЛЬЗОВАНИЕМ ПРОЦЕССА ПЛАЗМОХИМИЧЕСКОГО ТРАВЛЕНИЯ

Possible process options for thinning semiconductor substrates have been analyzed. Experiments have been conducted to assess the efficiency of plasma−chemical etching of (100) orientation single crystal germanium substrates used for growing heteroepitaxial structures of multi−cascade solar cells based on A3B5 semiconductor compounds. The specimens were etched on a reactive ion etching instrument with an induction type high−density plasma source in (SF6 : Ar = 2 : 1) gas mixture through various photoresist masks. For FP−383 photoresist masks with 2, 4 and 6.5 µm windows, the etched layer was 20 µm in depth. For a FN−11 photoresist mask with a 95 µm window, etching reached a depth of 58 µm. The FP−383 masks exhibited thinning from 1.5 to 0.87 µm, and the FN−11 mask thinned from 10 to 8 µm. We show that the etching rate which was 2.1−3.3 µm/min decreases with an increase in mask window width following a power law. We have concluded that plasma−chemical etching is a promising tool for improving the energy and mass parameters of multi−cascade solar cells with conventional and metamorphic structures at the final stage of their fabrication.Проанализированы возможные технологические варианты утонения полу-проводниковых подложек. Проведена экспериментальная оценка эффективности плазмохимического травления подложек монокристаллического германия с кристаллографической ориентацией (100), применяемых для выращивания гетероэпитаксиальных структур многокаскадных солнечных элементов на основе полупроводниковых соединений АIIIВV. Травление выполнено на установке реактивно−ионного травления с источником высокоплотной плазмы индукционного типа в газовой смеси (SF6 : Ar = 2 : 1) через различные фоторезистивные маски. Для масок на основе фоторезиста ФП−383 с шириной окна 2, 4 и 6,5 мкм травление выполнено на глубину 20 мкм. Для маски на основе фоторезиста ФН−11 с шириной окна 95 мкм травление выполнено на глубину 58 мкм. Отмечено уменьшение толщины маски на основе ФП−383 с 1,5 до 0,87 мкм, а также толщины маски на основе ФН−11 с 10 до 8 мкм. Установлено, что скорость травления, значения которой составили 2,1—3,3 мкм/мин, снижается с увеличением ширины окна маски по степенному закону. Сделан вывод о перспективности применения плазмохимического травления на заключительной стадии технологического процесса изготовления многокаскадных солнечных эле-ментов традиционной и метаморфной конструкций для улучшения энерго-массовых характеристик.

Hole traps and persistent photocapacitance in proton irradiated β-Ga2O3 films doped with Si

Hole traps in hydride vapor phase epitaxy β-Ga2O3 films were studied by deep level transient spectroscopy with electrical and optical excitation (DLTS and ODLTS) and by photocapacitance and temperature dependence measurements. Irradiation with 20 MeV protons creates deep electron and hole traps, a strong increase in photocapacitance, and prominent persistent photocapacitance that partly persists above room temperature. Three hole-trap-like signals H1 [self-trapped holes (STH)], H2 [electron capture barrier (ECB)], and H3, with activation energies 0.2 eV, 0.4 eV, 1.3 eV, respectively, were detected in ODLTS. The H1 (STH) feature is suggested to correspond to the transition of polaronic states of STH to mobile holes in the valence band. The broad H2 (ECB) feature is due to overcoming of the ECB of the centers responsible for persistent photocapacitance for temperatures below 250 K. The H3 peak is produced by detrapping of holes from Ev + 1.3 eV hole traps believed to be related to gallium vacancy acceptors. One more deep acceptor with optical ionization threshold near 2.3 eV is likely responsible for high temperature persistent photocapacitance surviving up to temperatures higher than 400 K. The latter traps show a significant barrier for capture of electrons

Effects of 5 MeV electron irradiation on deep traps and electroluminescence from near-UV InGaN/GaN single quantum well light-emitting diodes with and without InAlN superlattice underlayer

The electrical properties, electroluminescence (EL) power output and deep trap spectra were studied before and after 5 MeV electron irradiation of near-UV single-quantum-well (SQW) light-emitting diodes (LED) structures differing by the presence or absence of InAlN superlattice underlayers (InAlN SL UL). The presence of the underlayer is found to remarkably increase the EL output power and the radiation tolerance of LEDs, which correlates with a much lower and more slowly changing density of deep traps in the QW region with radiation dose, and the higher lifetime of charge carriers, manifested by higher short-circuit current and open-circuit voltage in current-voltage characteristics under illumination. The observed phenomena are explained by the capture of native defects segregated at the growing surface by In atoms in the underlayer which traps them in the underlayer and prevents their penetration into the QW region

Effects of 5 MeV electron irradiation on deep traps and electroluminescence from near-UV InGaN/GaN single quantum well light-emitting diodes with and without InAlN superlattice underlayer

The electrical properties, electroluminescence (EL) power output and deep trap spectra were studied before and after 5 MeV electron irradiation of near-UV single-quantum-well (SQW) light-emitting diodes (LED) structures differing by the presence or absence of InAlN superlattice underlayers (InAlN SL UL). The presence of the underlayer is found to remarkably increase the EL output power and the radiation tolerance of LEDs, which correlates with a much lower and more slowly changing density of deep traps in the QW region with radiation dose, and the higher lifetime of charge carriers, manifested by higher short-circuit current and open-circuit voltage in current-voltage characteristics under illumination. The observed phenomena are explained by the capture of native defects segregated at the growing surface by In atoms in the underlayer which traps them in the underlayer and prevents their penetration into the QW region

Effects of InAlN underlayer on deep traps detected in near-UV InGaN/GaN single quantum well light-emitting diodes

Two types of near-UV light-emitting diodes (LEDs) with an InGaN/GaN single quantum well (QW) differing only in the presence or absence of an underlayer (UL) consisting of an InAlN/GaN superlattice (SL) were examined. The InAlN-based ULs were previously shown to dramatically improve internal quantum efficiency of near-UV LEDs, via a decrease in the density of deep traps responsible for nonradiative recombination in the QW region. The main differences between samples with and without UL were (a) a higher compensation of Mg acceptors in the p-GaN:Mg contact layer of the sample without UL, which correlates with the presence of traps with an activation energy of 0.06 eV in the QW region, (b) the presence of deep electron traps with levels 0.6 eV below the conduction band edge (E-c) (ET1) and at E-c 0.77 eV (ET2) in the n-GaN spacer underneath the QW, and the presence of hole traps (HT1) in the QW, 0.73 eV above the valence band edge in the sample without UL (no traps could be detected in the sample with UL), and (c) a high density of deep traps with optical ionization energy close to 1.5 eV for the LEDs without UL. Irradiation with 5 MeV electrons led to a strong decrease in the electroluminescence (EL) intensity in the LEDs without UL, while for the samples with UL, such irradiation had little effect on the EL signal at high driving current, although the level of driving currents necessary to have a measurable EL signal increased by about an order of magnitude. This is despite the 5 times higher starting EL signal of the sample with UL. Irradiation also led to the appearance in the LEDs with UL of the ET1 and HT1 deep traps, but with concentration much lower than without the UL, and to a considerable increase in the Mg compensation ratio

Deep traps in InGaN/GaN single quantum well structures grown with and without InGaN underlayers

The electrical properties and deep trap spectra were compared for near-UV GaN/InGaN quantum well (QW) structures grown on free-standing GaN substrates. The structures differed by the presence or absence of a thin (110 nm) InGaN layer inserted between the high temperature GaN buffer and the QW region. Capacitance-voltage profiling with monochromatic illumination showed that in the InGaN underlayer (UL), the density of deep traps with optical threshold near 1.5 eV was much higher than in the QW and higher than for structures without InGaN. Irradiation with 5 MeV electrons strongly increased the concentration of these 1.5 eV traps in the QWs, with the increase more pronounced for samples without InGaN ULs. The observations are interpreted using the earlier proposed model explaining the impact of In-containing underlayers by segregation of native defects formed during growth of GaN near the surface and trapping of these surface defects by In atoms of the InGaN UL, thus preventing them from infiltrating the InGaN QW region. Deep level transient spectroscopy (DLTS) also revealed major differences in deep trap spectra in the QWs and underlying layers of the samples with and without InGaN ULs. Specifically, the introduction of the InGaN UL stimulates changing the dominant type of deep traps. Irradiation increases the densities of these traps, with the increase being more pronounced for samples without the InGaN UL. It is argued that light emitting diodes (LEDs) with InGaN UL should demonstrate a higher radiation tolerance than LEDs without InGaN UL. (C) 2020 Elsevier B.V. All rights reserved