{"id":{"repo_id":"aachen","oai_identifier":"oai:publications.rwth-aachen.de:59424"},"canonical_url":"https://search.dev.ndltd.org/etd/aachen/oai:publications.rwth-aachen.de:59424","repository":{"repo_id":"aachen","name":"RWTH Aachen University","base_url":"https://publications.rwth-aachen.de/oai2d"},"display":{"title":"MOVPE growth and characterization of Al Kappa Ga 1 - Kappa N/GaN heterostructures for HEMT application","abstract":"In this thesis the MOVPE growth of AlN, GaN and AlGaN/GaN heterostructures on sapphire substrates was investigated with respect to HEMT application. The prerequisites for excellent HEMT devices were defined with respect to their structural properties: the HEMT structure should consist of a highly resistive buffer layer, a highly conductive channel layer, have a smooth morphology and should exhibit good uniformity. An overview of the chemistry which governs the MOVPE of (Al)GaN was introduced in order to offer the basis for the interpretation of the experiments. Growth experiments were carried out at 50 and 200 mbar for the Al-containing nitrides and GaN, respectively, using trimethyl Al- and Ga- compounds and NH3 as the precursors and H2 as the carrier gas. The assessment of the layer quality was performed optically by in-situ reflectometry and ex-situ by PL, structurally by X-ray diffraction and RBS, morphologically by Nomarski microscopy, AFM and SEM, electrically by Hall effect measurements. First the variation of growth parameters during the nucleation and their effect on the characteristics of the successive buffer layer were investigated and the results are presented. It was found that the growth is kinetically limited at the typical temperatures (500 - 600øC) used for nucleation layer deposition with an activation energy of 14.5 kcal/mol. The nucleation layer thickness must be carefully tuned to an optimal value (in our case about 25 nm) in order to provide the optimal ratio between the number and the size of nuclei. For both AlN and GaN nucleation layers a strong interdependence between the group III and group V source flows as well as nucleation and annealing times was found. For AlN nucleation layer growth the optimal parameter window is smaller than for GaN. For high temperature GaN growth (1080 - 1140øC) two growth regimes were identified. Below 1110øC the growth rate is nearly independent of temperature, growth being diffusion controlled. Above this temperature a drastic linear decrease of the growth rate is observed indicating that GaN decomposition plays an important role. However, with increasing temperature the electrical and optical characteristics of the layers improve. The optimised GaN buffers were employed for the growth of AlGaN/GaN HEMT structures. The influence of the Al content on the layer properties was investigated. It was found, that with increasing Al content the sheet carrier concentration of the 2DEG increases. On the other hand, the electron mobility at 77K is decreased due to a roughening of the AlGaN/GaN interface. The surface roughness is within the range tolerated for device processing. State-of-the-art electrical properties and the existence of a 2DEG could be demonstrated. It was demonstrated by modelling and experiments that in horizontal reactors, in which the NH3/carrier gas (H2) mixture is let into the reactor separately and closer to the susceptor than the MO/carrier gas mixture, an increase of the carrier gas flow ratio between MO and NH3 sides leads to a slight improvement in layer homogeneity and an increased growth efficiency. Additionally, the influence of the gas inlet design on growth rate was analysed. A major problem for nitride deposition is the reproducible growth of layers and two factors were found responsible. The surface temperature changes unintentionally form run to run, fact which affects the growth. The second factor which negatively influences the growth are the deposits located on the reactor ceiling which behave as a catalytic surface depleting the chemical species contributing to the growth. Therefore it will only be possible to deposit layers reproducibly when parasitic deposits are avoided and the true substrate temperature is controlled.","abstract_html":"In this thesis the MOVPE growth of AlN, GaN and AlGaN/GaN heterostructures on sapphire substrates was investigated with respect to HEMT application. The prerequisites for excellent HEMT devices were defined with respect to their structural properties: the HEMT structure should consist of a highly resistive buffer layer, a highly conductive channel layer, have a smooth morphology and should exhibit good uniformity. An overview of the chemistry which governs the MOVPE of (Al)GaN was introduced in order to offer the basis for the interpretation of the experiments. Growth experiments were carried out at 50 and 200 mbar for the Al-containing nitrides and GaN, respectively, using trimethyl Al- and Ga- compounds and NH3 as the precursors and H2 as the carrier gas. The assessment of the layer quality was performed optically by in-situ reflectometry and ex-situ by PL, structurally by X-ray diffraction and RBS, morphologically by Nomarski microscopy, AFM and SEM, electrically by Hall effect measurements. First the variation of growth parameters during the nucleation and their effect on the characteristics of the successive buffer layer were investigated and the results are presented. It was found that the growth is kinetically limited at the typical temperatures (500 - 600øC) used for nucleation layer deposition with an activation energy of 14.5 kcal/mol. The nucleation layer thickness must be carefully tuned to an optimal value (in our case about 25 nm) in order to provide the optimal ratio between the number and the size of nuclei. For both AlN and GaN nucleation layers a strong interdependence between the group III and group V source flows as well as nucleation and annealing times was found. For AlN nucleation layer growth the optimal parameter window is smaller than for GaN. For high temperature GaN growth (1080 - 1140øC) two growth regimes were identified. Below 1110øC the growth rate is nearly independent of temperature, growth being diffusion controlled. Above this temperature a drastic linear decrease of the growth rate is observed indicating that GaN decomposition plays an important role. However, with increasing temperature the electrical and optical characteristics of the layers improve. The optimised GaN buffers were employed for the growth of AlGaN/GaN HEMT structures. The influence of the Al content on the layer properties was investigated. It was found, that with increasing Al content the sheet carrier concentration of the 2DEG increases. On the other hand, the electron mobility at 77K is decreased due to a roughening of the AlGaN/GaN interface. The surface roughness is within the range tolerated for device processing. State-of-the-art electrical properties and the existence of a 2DEG could be demonstrated. It was demonstrated by modelling and experiments that in horizontal reactors, in which the NH3/carrier gas (H2) mixture is let into the reactor separately and closer to the susceptor than the MO/carrier gas mixture, an increase of the carrier gas flow ratio between MO and NH3 sides leads to a slight improvement in layer homogeneity and an increased growth efficiency. Additionally, the influence of the gas inlet design on growth rate was analysed. A major problem for nitride deposition is the reproducible growth of layers and two factors were found responsible. The surface temperature changes unintentionally form run to run, fact which affects the growth. The second factor which negatively influences the growth are the deposits located on the reactor ceiling which behave as a catalytic surface depleting the chemical species contributing to the growth. Therefore it will only be possible to deposit layers reproducibly when parasitic deposits are avoided and the true substrate temperature is controlled.","abstract_has_math":false,"creators":["Kaluza, Nicoleta Elena"],"institution":"Publikationsserver der RWTH Aachen University","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Lüth, Hans"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2003,"date_issued":"2003","date_published":"2003","updated_at":"2026-07-30T19:42:39Z","subjects":["info:eu-repo/classification/ddc/540","Verbindungshalbleiter","Borgruppennitride","Heterostruktur","MOCVD-Verfahren","Saphir","Substrat <Mikroelektronik>","Chemie","MOVPE","GaN","HEMT","Nitrides","MOCVD"],"languages":["eng"],"rights":["info:eu-repo/semantics/openAccess"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-121211%22"],"render_values":[{"text":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-121211%22","href":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-121211%22","code":true}]}]},"links":{"outbound_url":"https://publications.rwth-aachen.de/record/59424","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Lüth, Hans"]},{"key":"dc:creator","label":"Author","values":["Kaluza, Nicoleta Elena"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:coverage","label":"Dc Coverage","values":["DE"]},{"key":"dc:date","label":"Dc Date","values":["2003"]},{"key":"dc:publisher","label":"Institution","values":["Publikationsserver der RWTH Aachen University"]},{"key":"dc:relation","label":"Dc Relation","values":["info:eu-repo/semantics/altIdentifier/doi/10.18154/RWTH-CONV-121211","info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-8296"]},{"key":"dc:type","label":"Dc Type","values":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["info:eu-repo/classification/ddc/540","Verbindungshalbleiter","Borgruppennitride","Heterostruktur","MOCVD-Verfahren","Saphir","Substrat <Mikroelektronik>","Chemie","MOVPE","GaN","HEMT","Nitrides","MOCVD"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["info:eu-repo/semantics/openAccess"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/record/59424","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-121211%22"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["In this thesis the MOVPE growth of AlN, GaN and AlGaN/GaN heterostructures on sapphire substrates was investigated with respect to HEMT application. The prerequisites for excellent HEMT devices were defined with respect to their structural properties: the HEMT structure should consist of a highly resistive buffer layer, a highly conductive channel layer, have a smooth morphology and should exhibit good uniformity. An overview of the chemistry which governs the MOVPE of (Al)GaN was introduced in order to offer the basis for the interpretation of the experiments. Growth experiments were carried out at 50 and 200 mbar for the Al-containing nitrides and GaN, respectively, using trimethyl Al- and Ga- compounds and NH3 as the precursors and H2 as the carrier gas. The assessment of the layer quality was performed optically by in-situ reflectometry and ex-situ by PL, structurally by X-ray diffraction and RBS, morphologically by Nomarski microscopy, AFM and SEM, electrically by Hall effect measurements. First the variation of growth parameters during the nucleation and their effect on the characteristics of the successive buffer layer were investigated and the results are presented. It was found that the growth is kinetically limited at the typical temperatures (500 - 600øC) used for nucleation layer deposition with an activation energy of 14.5 kcal/mol. The nucleation layer thickness must be carefully tuned to an optimal value (in our case about 25 nm) in order to provide the optimal ratio between the number and the size of nuclei. For both AlN and GaN nucleation layers a strong interdependence between the group III and group V source flows as well as nucleation and annealing times was found. For AlN nucleation layer growth the optimal parameter window is smaller than for GaN. For high temperature GaN growth (1080 - 1140øC) two growth regimes were identified. Below 1110øC the growth rate is nearly independent of temperature, growth being diffusion controlled. Above this temperature a drastic linear decrease of the growth rate is observed indicating that GaN decomposition plays an important role. However, with increasing temperature the electrical and optical characteristics of the layers improve. The optimised GaN buffers were employed for the growth of AlGaN/GaN HEMT structures. The influence of the Al content on the layer properties was investigated. It was found, that with increasing Al content the sheet carrier concentration of the 2DEG increases. On the other hand, the electron mobility at 77K is decreased due to a roughening of the AlGaN/GaN interface. The surface roughness is within the range tolerated for device processing. State-of-the-art electrical properties and the existence of a 2DEG could be demonstrated. It was demonstrated by modelling and experiments that in horizontal reactors, in which the NH3/carrier gas (H2) mixture is let into the reactor separately and closer to the susceptor than the MO/carrier gas mixture, an increase of the carrier gas flow ratio between MO and NH3 sides leads to a slight improvement in layer homogeneity and an increased growth efficiency. Additionally, the influence of the gas inlet design on growth rate was analysed. A major problem for nitride deposition is the reproducible growth of layers and two factors were found responsible. The surface temperature changes unintentionally form run to run, fact which affects the growth. The second factor which negatively influences the growth are the deposits located on the reactor ceiling which behave as a catalytic surface depleting the chemical species contributing to the growth. Therefore it will only be possible to deposit layers reproducibly when parasitic deposits are avoided and the true substrate temperature is controlled."]},{"key":"dc:source","label":"Dc Source","values":["Aachen : Publikationsserver der RWTH Aachen University II, 178 S. : Ill., graph. Darst. (2003). doi:10.18154/RWTH-CONV-121211 = Aachen, Techn. Hochsch., Diss., 2003"]},{"key":"dc:title","label":"Title","values":["MOVPE growth and characterization of Al Kappa Ga 1 - Kappa N/GaN heterostructures for HEMT application"]}]}],"canonical_facts":{"dc:contributor":["Lüth, Hans"],"dc:coverage":["DE"],"dc:creator":["Kaluza, Nicoleta Elena"],"dc:date":["2003"],"dc:description":["In this thesis the MOVPE growth of AlN, GaN and AlGaN/GaN heterostructures on sapphire substrates was investigated with respect to HEMT application. The prerequisites for excellent HEMT devices were defined with respect to their structural properties: the HEMT structure should consist of a highly resistive buffer layer, a highly conductive channel layer, have a smooth morphology and should exhibit good uniformity. An overview of the chemistry which governs the MOVPE of (Al)GaN was introduced in order to offer the basis for the interpretation of the experiments. Growth experiments were carried out at 50 and 200 mbar for the Al-containing nitrides and GaN, respectively, using trimethyl Al- and Ga- compounds and NH3 as the precursors and H2 as the carrier gas. The assessment of the layer quality was performed optically by in-situ reflectometry and ex-situ by PL, structurally by X-ray diffraction and RBS, morphologically by Nomarski microscopy, AFM and SEM, electrically by Hall effect measurements. First the variation of growth parameters during the nucleation and their effect on the characteristics of the successive buffer layer were investigated and the results are presented. It was found that the growth is kinetically limited at the typical temperatures (500 - 600øC) used for nucleation layer deposition with an activation energy of 14.5 kcal/mol. The nucleation layer thickness must be carefully tuned to an optimal value (in our case about 25 nm) in order to provide the optimal ratio between the number and the size of nuclei. For both AlN and GaN nucleation layers a strong interdependence between the group III and group V source flows as well as nucleation and annealing times was found. For AlN nucleation layer growth the optimal parameter window is smaller than for GaN. For high temperature GaN growth (1080 - 1140øC) two growth regimes were identified. Below 1110øC the growth rate is nearly independent of temperature, growth being diffusion controlled. Above this temperature a drastic linear decrease of the growth rate is observed indicating that GaN decomposition plays an important role. However, with increasing temperature the electrical and optical characteristics of the layers improve. The optimised GaN buffers were employed for the growth of AlGaN/GaN HEMT structures. The influence of the Al content on the layer properties was investigated. It was found, that with increasing Al content the sheet carrier concentration of the 2DEG increases. On the other hand, the electron mobility at 77K is decreased due to a roughening of the AlGaN/GaN interface. The surface roughness is within the range tolerated for device processing. State-of-the-art electrical properties and the existence of a 2DEG could be demonstrated. It was demonstrated by modelling and experiments that in horizontal reactors, in which the NH3/carrier gas (H2) mixture is let into the reactor separately and closer to the susceptor than the MO/carrier gas mixture, an increase of the carrier gas flow ratio between MO and NH3 sides leads to a slight improvement in layer homogeneity and an increased growth efficiency. Additionally, the influence of the gas inlet design on growth rate was analysed. A major problem for nitride deposition is the reproducible growth of layers and two factors were found responsible. The surface temperature changes unintentionally form run to run, fact which affects the growth. The second factor which negatively influences the growth are the deposits located on the reactor ceiling which behave as a catalytic surface depleting the chemical species contributing to the growth. Therefore it will only be possible to deposit layers reproducibly when parasitic deposits are avoided and the true substrate temperature is controlled."],"dc:identifier":["https://publications.rwth-aachen.de/record/59424","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-121211%22"],"dc:language":["eng"],"dc:publisher":["Publikationsserver der RWTH Aachen University"],"dc:relation":["info:eu-repo/semantics/altIdentifier/doi/10.18154/RWTH-CONV-121211","info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-8296"],"dc:rights":["info:eu-repo/semantics/openAccess"],"dc:source":["Aachen : Publikationsserver der RWTH Aachen University II, 178 S. : Ill., graph. Darst. (2003). doi:10.18154/RWTH-CONV-121211 = Aachen, Techn. Hochsch., Diss., 2003"],"dc:subject":["info:eu-repo/classification/ddc/540","Verbindungshalbleiter","Borgruppennitride","Heterostruktur","MOCVD-Verfahren","Saphir","Substrat <Mikroelektronik>","Chemie","MOVPE","GaN","HEMT","Nitrides","MOCVD"],"dc:title":["MOVPE growth and characterization of Al Kappa Ga 1 - Kappa N/GaN heterostructures for HEMT application"],"dc:type":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]},"updated_at":"2026-07-30T19:42:39Z"}