A femtosecond laser focused inside bulk GaN was used to slice a thin GaN film with an epitaxial d... more A femtosecond laser focused inside bulk GaN was used to slice a thin GaN film with an epitaxial device structure from a bulk GaN substrate. The demonstrated laser slicing lift-off process did not require any special release layers in the epitaxial structure. GaN film with a thickness of 5 um and an InGaN LED epitaxial device structure was lifted off a GaN substrate and transferred onto a copper substrate. The electroluminescence of the LED chip after the laser slicing lift-off was demonstrated.
IEEE Conference of Russian Young Researchers in Electrical and Electronic Engineering (EIConRus) , 2019
Cracking of thick GaN films on sapphire substrates during the cooling down after the growth was s... more Cracking of thick GaN films on sapphire substrates during the cooling down after the growth was studied. The cracking was suppressed by increasing the film-to-substrate thickness ratio and by using an intermediate carbon buffer layer, that reduced the binding energy between the GaN film and the substrate. Wafer-scale self-separation of thick GaN films has been demonstrated.
GaN thick films, grown on specially patterned 2" sapphire substrates by HVPE methods have lower b... more GaN thick films, grown on specially patterned 2" sapphire substrates by HVPE methods have lower bowing and are less susceptible to fracture then ones, grown on unpatterned substrates under the same growth conditions. Numerical calculation shows good agreement with experiments. Such substrates could be an alternative to expen-sive GaN wafers sliced from GaN boules.
The intense absorption of CO 2 laser radiation in sapphire is used to separate GaN films from GaN... more The intense absorption of CO 2 laser radiation in sapphire is used to separate GaN films from GaN templates on sapphire. Scanning of the sapphire substrate by the laser leads to the thermal dissociation of GaN at the GaN/sapphire interface and to the detachment of GaN films from the sapphire. The threshold density of the laser energy at which n-GaN started to dissociate is 1.6 ± 0.5 J/cm 2. The mechanical-stress distribution and the surface morphology of GaN films and sapphire substrates before and after laser lift-off are studied by Raman spectroscopy, atomic-force microscopy, and scanning electron microscopy. A vertical Schottky diode with a forward current density of 100 A/cm 2 at a voltage of 2 V and a maximum reverse voltage of 150 V is fabricated on the basis of a 9-μm-thick detached n-GaN film.
The physical and technological basics of the method used to lift off lightly and moderately doped... more The physical and technological basics of the method used to lift off lightly and moderately doped n-GaN films from heavily doped n +-GaN substrates are considered. The detachment method is based on the free-charge-carrier absorption of IR laser light, which is substantially higher in n +-GaN films.
The quantum efficiency of GaN-based light-emitting diodes (LEDs) is investigated at temperatures ... more The quantum efficiency of GaN-based light-emitting diodes (LEDs) is investigated at temperatures 77–300 K. It is found that the efficiency droop is due to a decrease in the internal quantum efficiency (IQE) in the low-energy part of the emission spectrum. The efficiency starts to decrease at a temperature independent forward voltage of Umax≈2.9 V. At this voltage tunneling current through the LED-structure begins to dominate. It is suggested that the external quantum efficiency droop is related to reduction of the IQE due to tunneling leakage of carriers from the quantum well (QW) to defect states in barriers, and to reduction of the injection efficiency by excess tunneling current under QW through deep defect states in barriers.
The quantum efficiency of GaN LED structures has been studied at various temperatures and biases.... more The quantum efficiency of GaN LED structures has been studied at various temperatures and biases. It was found that an efficiency falloff is observed with increasing current density and, simultaneously, the tunnel component of the current through the LED grows and the quasi-Fermi levels reach the mobility edge in the InGaN active layer. It is shown that the internal quantum efficiency falloff with increasing current density is due to the carrier leakage from the quantum well as a result of tunnel transitions from its band-tail states to local defect-related energy levels within the energy gaps of the barrier layers.
GaN films with thickness up to 3 mm were grown by halide vapour phase epitaxy method. Two growth ... more GaN films with thickness up to 3 mm were grown by halide vapour phase epitaxy method. Two growth modes were observed: the high temperature (HT) mode and the low temperature (LT) mode. Films grown in HT mode had smooth surface, however the growth stress was high and caused cracking. Films grown in LT mode had rough surface with high density of V‐defects (pits), however, such films were crack‐free. The influence of growth parameters on the pit shape and evolution was investigated. Origins of pits formation and process of pit overgrowth are discussed. Crack‐free films with smooth surface and reduced density of pits were grown using combination of the LT and HT growth modes.
GaN films with thicknesses up to 3 mm were grown in two custom-made halide vapor phase epitaxy (H... more GaN films with thicknesses up to 3 mm were grown in two custom-made halide vapor phase epitaxy (HVPE) reactors. V-shaped defects (pits) with densities from 1 to 100 cm À2 were found on the surfaces of the films. Origins of pit formation and the process of pit overgrowth were studied by analysing the kinematics of pit evolution. Two mechanisms of pit overgrowth were observed. Pits can be overgrown intentionally by varying growth parameters to increase the growth rate of pit facets. Pits can overgrow spontaneously if a fast-growing facet nucleates at their bottom under constant growth conditions.
Hydride Vapor Phase Epitaxy is a promising method for the industrial production of GaN substrates... more Hydride Vapor Phase Epitaxy is a promising method for the industrial production of GaN substrates. However, no HVPE reactors for the GaN and AlN bulk layer deposition are available on the market. We have developed a HVPE reactor for mass production of bulk GaN and AlN epitaxial layers with thickness up to 10 mm and diameter of 50 mm. A load-lock vacuum chamber and dry in-situ cleaning of growth chamber and substrate holder were implemented to improve the process reproducibility. High-capacity precursor sources have been developed to implement non-stop growth of layers with total thickness of 10 mm and higher. Freestanding GaN crystals with thickness of 5 mm and diameter of 50 mm have been grown with the reactor.
The effect of growth parameters on stress in thick GaN films grown on sapphire by HVPE method was... more The effect of growth parameters on stress in thick GaN films grown on sapphire by HVPE method was investigated. We have found two modes of growth with different growth stress. Films grown in one mode have rough surfaces and low stress. The second mode leads to smooth surfaces but the films contain many cracks due to high growth stress. A combination of these modes allows growth of films without cracks and with smooth surfaces.
A femtosecond laser focused inside bulk GaN was used to slice a thin GaN film with an epitaxial d... more A femtosecond laser focused inside bulk GaN was used to slice a thin GaN film with an epitaxial device structure from a bulk GaN substrate. The demonstrated laser slicing lift-off process did not require any special release layers in the epitaxial structure. GaN film with a thickness of 5 um and an InGaN LED epitaxial device structure was lifted off a GaN substrate and transferred onto a copper substrate. The electroluminescence of the LED chip after the laser slicing lift-off was demonstrated.
IEEE Conference of Russian Young Researchers in Electrical and Electronic Engineering (EIConRus) , 2019
Cracking of thick GaN films on sapphire substrates during the cooling down after the growth was s... more Cracking of thick GaN films on sapphire substrates during the cooling down after the growth was studied. The cracking was suppressed by increasing the film-to-substrate thickness ratio and by using an intermediate carbon buffer layer, that reduced the binding energy between the GaN film and the substrate. Wafer-scale self-separation of thick GaN films has been demonstrated.
GaN thick films, grown on specially patterned 2" sapphire substrates by HVPE methods have lower b... more GaN thick films, grown on specially patterned 2" sapphire substrates by HVPE methods have lower bowing and are less susceptible to fracture then ones, grown on unpatterned substrates under the same growth conditions. Numerical calculation shows good agreement with experiments. Such substrates could be an alternative to expen-sive GaN wafers sliced from GaN boules.
The intense absorption of CO 2 laser radiation in sapphire is used to separate GaN films from GaN... more The intense absorption of CO 2 laser radiation in sapphire is used to separate GaN films from GaN templates on sapphire. Scanning of the sapphire substrate by the laser leads to the thermal dissociation of GaN at the GaN/sapphire interface and to the detachment of GaN films from the sapphire. The threshold density of the laser energy at which n-GaN started to dissociate is 1.6 ± 0.5 J/cm 2. The mechanical-stress distribution and the surface morphology of GaN films and sapphire substrates before and after laser lift-off are studied by Raman spectroscopy, atomic-force microscopy, and scanning electron microscopy. A vertical Schottky diode with a forward current density of 100 A/cm 2 at a voltage of 2 V and a maximum reverse voltage of 150 V is fabricated on the basis of a 9-μm-thick detached n-GaN film.
The physical and technological basics of the method used to lift off lightly and moderately doped... more The physical and technological basics of the method used to lift off lightly and moderately doped n-GaN films from heavily doped n +-GaN substrates are considered. The detachment method is based on the free-charge-carrier absorption of IR laser light, which is substantially higher in n +-GaN films.
The quantum efficiency of GaN-based light-emitting diodes (LEDs) is investigated at temperatures ... more The quantum efficiency of GaN-based light-emitting diodes (LEDs) is investigated at temperatures 77–300 K. It is found that the efficiency droop is due to a decrease in the internal quantum efficiency (IQE) in the low-energy part of the emission spectrum. The efficiency starts to decrease at a temperature independent forward voltage of Umax≈2.9 V. At this voltage tunneling current through the LED-structure begins to dominate. It is suggested that the external quantum efficiency droop is related to reduction of the IQE due to tunneling leakage of carriers from the quantum well (QW) to defect states in barriers, and to reduction of the injection efficiency by excess tunneling current under QW through deep defect states in barriers.
The quantum efficiency of GaN LED structures has been studied at various temperatures and biases.... more The quantum efficiency of GaN LED structures has been studied at various temperatures and biases. It was found that an efficiency falloff is observed with increasing current density and, simultaneously, the tunnel component of the current through the LED grows and the quasi-Fermi levels reach the mobility edge in the InGaN active layer. It is shown that the internal quantum efficiency falloff with increasing current density is due to the carrier leakage from the quantum well as a result of tunnel transitions from its band-tail states to local defect-related energy levels within the energy gaps of the barrier layers.
GaN films with thickness up to 3 mm were grown by halide vapour phase epitaxy method. Two growth ... more GaN films with thickness up to 3 mm were grown by halide vapour phase epitaxy method. Two growth modes were observed: the high temperature (HT) mode and the low temperature (LT) mode. Films grown in HT mode had smooth surface, however the growth stress was high and caused cracking. Films grown in LT mode had rough surface with high density of V‐defects (pits), however, such films were crack‐free. The influence of growth parameters on the pit shape and evolution was investigated. Origins of pits formation and process of pit overgrowth are discussed. Crack‐free films with smooth surface and reduced density of pits were grown using combination of the LT and HT growth modes.
GaN films with thicknesses up to 3 mm were grown in two custom-made halide vapor phase epitaxy (H... more GaN films with thicknesses up to 3 mm were grown in two custom-made halide vapor phase epitaxy (HVPE) reactors. V-shaped defects (pits) with densities from 1 to 100 cm À2 were found on the surfaces of the films. Origins of pit formation and the process of pit overgrowth were studied by analysing the kinematics of pit evolution. Two mechanisms of pit overgrowth were observed. Pits can be overgrown intentionally by varying growth parameters to increase the growth rate of pit facets. Pits can overgrow spontaneously if a fast-growing facet nucleates at their bottom under constant growth conditions.
Hydride Vapor Phase Epitaxy is a promising method for the industrial production of GaN substrates... more Hydride Vapor Phase Epitaxy is a promising method for the industrial production of GaN substrates. However, no HVPE reactors for the GaN and AlN bulk layer deposition are available on the market. We have developed a HVPE reactor for mass production of bulk GaN and AlN epitaxial layers with thickness up to 10 mm and diameter of 50 mm. A load-lock vacuum chamber and dry in-situ cleaning of growth chamber and substrate holder were implemented to improve the process reproducibility. High-capacity precursor sources have been developed to implement non-stop growth of layers with total thickness of 10 mm and higher. Freestanding GaN crystals with thickness of 5 mm and diameter of 50 mm have been grown with the reactor.
The effect of growth parameters on stress in thick GaN films grown on sapphire by HVPE method was... more The effect of growth parameters on stress in thick GaN films grown on sapphire by HVPE method was investigated. We have found two modes of growth with different growth stress. Films grown in one mode have rough surfaces and low stress. The second mode leads to smooth surfaces but the films contain many cracks due to high growth stress. A combination of these modes allows growth of films without cracks and with smooth surfaces.
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Papers by Andrey Zubrilov