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Valence band engineering in semiconductor lasers / Ali Ghiti 

Public ISBD Titre : Valence band engineering in semiconductor lasers Type de document : texte imprimé Auteurs : Ali Ghiti, Auteur Editeur : University of Surrey Année de publication : 1990 Importance : 136 f. Présentation : ill. Format : 30 cm. Note générale : Thèse de Doctorat : Philosophy : Royaume-Uni, University of Surrey : 1990 Annexe f. 137 - 141 . Bibliogr. f. 142 - 151 Langues : Anglais (eng) Mots-clés : Semiconductor  laser Valence  band  engineering Strain Quantum  confinement Strained-layer  lasers Index. décimale : D001090 Résumé : This thesis is concerned with the improvement of semiconductor laser characteristics using valence band engineering. We first show that the combination of strain and quantum confinement can confer considerable advantages to long wavelength lasers. With sufficient built-in strain, the highest hole subband has a low effective mass and is well separated from the lower bands. The low effective mass reduces the carrier density needed for population inversion and leads to the virtual elimination of two important loss mechanisms: Auger recombination and intervalence band absorption. We propose a specific strained-layer 1.55μm structure that can reduce the threshold current density and its temperature dependence and increase the luminescent efficiency. The presence of strain can also lead to an enhancement of the relaxation oscillation frequency due to the higher differentialgain when compared to lattice-matched structures. The linewidth enhancement factor is also predicted to be reduced. Such strained-layer lasers could be of major significance for long distance optical communication. However, the long term stability of these structures, although promising, has still to be fully assessed. In view of this, we suggest that growth of unstrained structures could provide the light-hole cap to the valence band needed for laser operation. We find that the threshold current density in thin lasers could be reduced while the polarisation selection of TE modes could be improved compared to equivalent (001) lasers. Finally, we consider the effects of crystal orientation and of strain on the exciton binding energy. Valence band engineering in semiconductor lasers [texte imprimé] / Ali Ghiti, Auteur . - [S.l.] : University of Surrey, 1990 . - 136 f. : ill. ; 30 cm. Thèse de Doctorat : Philosophy : Royaume-Uni, University of Surrey : 1990 Annexe f. 137 - 141 . Bibliogr. f. 142 - 151 Langues : Anglais (eng) Mots-clés : Semiconductor  laser Valence  band  engineering Strain Quantum  confinement Strained-layer  lasers Index. décimale : D001090 Résumé : This thesis is concerned with the improvement of semiconductor laser characteristics using valence band engineering. We first show that the combination of strain and quantum confinement can confer considerable advantages to long wavelength lasers. With sufficient built-in strain, the highest hole subband has a low effective mass and is well separated from the lower bands. The low effective mass reduces the carrier density needed for population inversion and leads to the virtual elimination of two important loss mechanisms: Auger recombination and intervalence band absorption. We propose a specific strained-layer 1.55μm structure that can reduce the threshold current density and its temperature dependence and increase the luminescent efficiency. The presence of strain can also lead to an enhancement of the relaxation oscillation frequency due to the higher differentialgain when compared to lattice-matched structures. The linewidth enhancement factor is also predicted to be reduced. Such strained-layer lasers could be of major significance for long distance optical communication. However, the long term stability of these structures, although promising, has still to be fully assessed. In view of this, we suggest that growth of unstrained structures could provide the light-hole cap to the valence band needed for laser operation. We find that the threshold current density in thin lasers could be reduced while the polarisation selection of TE modes could be improved compared to equivalent (001) lasers. Finally, we consider the effects of crystal orientation and of strain on the exciton binding energy.

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Code-barres	Cote	Support	Localisation	Section	Disponibilité	Spécialité	Etat_Exemplaire
D001090	D001090	Papier	Bibliothèque centrale	Thèse de Doctorat	Disponible

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GHITI.Ali.pdf URL

Determination of bone density using photon scattering methods / Tewfik Baba Hamed 

Public ISBD Titre : Determination of bone density using photon scattering methods Type de document : texte imprimé Auteurs : Tewfik Baba Hamed, Auteur ; Nicholas M. Spyrou, Directeur de thèse Editeur : University of Surrey Année de publication : 1986 Importance : 48 f. Présentation : ill. Format : 30 cm. Note générale : Mémoire de Master : Medical Physics : Angleterre, University of Surrey : 1986 Annexe f. 50 - 65 . Bibliogr. f. 66 - 68 Langues : Anglais (eng) Mots-clés : Scattered  photons Bone  density Ratio Narrow  beam  geometry Transmission  photons Index. décimale : Ms00486 Résumé : Various diagnostic methods used in detrmining bone status are reviewed. Two methods using scattered photons for determination of bone density have been studied. The first involved the measurement of the ratio of coherent to Compton scattered photons from ²⁴¹Am using narrow beam geometry with an intrinsic germanium detector. The second method was based on the measurement of the ratio of coherent to transmission photons from the same experimental configuration used in the previous method. Solutions of K₂HPO₄ of known densities (1.0 - 1.660 x 10-³ g/mm³) were used to simulate trabecular bones. In both cases a high correlation between these ratios and bone sample densities was found. The results also showed that the coherent to transmission ratio gives a higher sensitivity than the coherent to Compton ratio method in the range of scattering angles used (30° - 90°). Determination of bone density using photon scattering methods [texte imprimé] / Tewfik Baba Hamed, Auteur ; Nicholas M. Spyrou, Directeur de thèse . - [S.l.] : University of Surrey, 1986 . - 48 f. : ill. ; 30 cm. Mémoire de Master : Medical Physics : Angleterre, University of Surrey : 1986 Annexe f. 50 - 65 . Bibliogr. f. 66 - 68 Langues : Anglais (eng) Mots-clés : Scattered  photons Bone  density Ratio Narrow  beam  geometry Transmission  photons Index. décimale : Ms00486 Résumé : Various diagnostic methods used in detrmining bone status are reviewed. Two methods using scattered photons for determination of bone density have been studied. The first involved the measurement of the ratio of coherent to Compton scattered photons from ²⁴¹Am using narrow beam geometry with an intrinsic germanium detector. The second method was based on the measurement of the ratio of coherent to transmission photons from the same experimental configuration used in the previous method. Solutions of K₂HPO₄ of known densities (1.0 - 1.660 x 10-³ g/mm³) were used to simulate trabecular bones. In both cases a high correlation between these ratios and bone sample densities was found. The results also showed that the coherent to transmission ratio gives a higher sensitivity than the coherent to Compton ratio method in the range of scattering angles used (30° - 90°).

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Code-barres	Cote	Support	Localisation	Section	Disponibilité	Spécialité	Etat_Exemplaire
Ms00486	Ms00486	Papier	Bibliothèque centrale	Mémoire de Master	Disponible

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BABA-HAMED.Tewfik.pdf URL

Rapid thermal annealing of donor implants in gallium arsenide / Rachid Bensalem 

Public ISBD Titre : Rapid thermal annealing of donor implants in gallium arsenide Type de document : texte imprimé Auteurs : Rachid Bensalem, Auteur ; Brian J. Sealy, Directeur de thèse Editeur : University of Surrey Année de publication : 1986 Importance : 181 f. Présentation : ill. Format : 30 cm. Note générale : Thèse de Doctorat : Microelectronics : Angleterre, University of Surrey : 1986 Bibliogr. f. 182 - 188 . Annexes Langues : Anglais (eng) Mots-clés : Rapid  thermal  annealing n+-surface  layers Selenium-implanted  GaAs van  der  Pauw  measurements Index. décimale : D004086 Résumé : Rapid thermal annealing was used to produce n+ surface layers in tin- and selenium-implanted GaAs. Hall effect and differential Van der Pauw measurements were performed and peak electron carrier concentrations of about 9 x 10¹⁸ cm-³ with corresponding sheet resistivities as low as 28 Ω/□, were achieved for high-dose, room-temperature Sn and Se implants. To realise this, development of new encapsulants and improvements to existing annealing methods were made. A novel method of depositing evaporated AIN for protecting the GaAs surface has been developed. This consists of the evaporation of Al in the presence of pure ammonia gas or an aqueous NH₃/N₂ gas mixture. The evaporated AIN layers were characterised using RBS and RHEED techniques and found to consist mainly of Al, N and O (as contaminant). These layers were used to successfully encapsulate GaAs at temperatures of up to 1100°C which is well above 950°C, the characteristic maximum useful temperature achieved using the existing CVD Si₃N₄. A double-layer encapsulant, consisting of ≈ 300 CVD Si₃N₄ plus 600 evaporated AIN was also developed and found to withstand even higher temperatures (≈1150°C) and to provide more reliable and reproducible results than either AIN or Si₃N₄ when used singly. A double graphite strip heater was developed in order to improve the accuracy of annealing temperature and time measurements. This method was compared to existing annealing methods (single graphite strip, incoherent light and electron beam annealers) and was found superior in terms of temperature accuracy and reproducibility. A simple thermodynamic theory has been developed to explain the incorporation of Sn and Se implanted into GaAs using results obtained from a detailed study of electrical properties measured as a function of annealing temperature and time for 1 x 10¹⁴ cm-² dose implanted at an energy of 300 keV and RT. The electrical activity was found to increase with time and temperature but for sufficiently long times, this activity saturates for a given temperature. Detailed analysis of the data produced: i) an activation energy of 1.2 ± 0.1 eV which is suggested to be that required to remove Sn or Se from a complex defect where it is inactive or compensated and subsequently place it on an appropriate vacancy where it acts as a donor and, ii) activation energies of diffusion of 2.5 ± 0.1 eV and 4.3 ± 0.4 eVfor Sn and Se implants in GaAs, respectively. Rapid thermal annealing of donor implants in gallium arsenide [texte imprimé] / Rachid Bensalem, Auteur ; Brian J. Sealy, Directeur de thèse . - [S.l.] : University of Surrey, 1986 . - 181 f. : ill. ; 30 cm. Thèse de Doctorat : Microelectronics : Angleterre, University of Surrey : 1986 Bibliogr. f. 182 - 188 . Annexes Langues : Anglais (eng) Mots-clés : Rapid  thermal  annealing n+-surface  layers Selenium-implanted  GaAs van  der  Pauw  measurements Index. décimale : D004086 Résumé : Rapid thermal annealing was used to produce n+ surface layers in tin- and selenium-implanted GaAs. Hall effect and differential Van der Pauw measurements were performed and peak electron carrier concentrations of about 9 x 10¹⁸ cm-³ with corresponding sheet resistivities as low as 28 Ω/□, were achieved for high-dose, room-temperature Sn and Se implants. To realise this, development of new encapsulants and improvements to existing annealing methods were made. A novel method of depositing evaporated AIN for protecting the GaAs surface has been developed. This consists of the evaporation of Al in the presence of pure ammonia gas or an aqueous NH₃/N₂ gas mixture. The evaporated AIN layers were characterised using RBS and RHEED techniques and found to consist mainly of Al, N and O (as contaminant). These layers were used to successfully encapsulate GaAs at temperatures of up to 1100°C which is well above 950°C, the characteristic maximum useful temperature achieved using the existing CVD Si₃N₄. A double-layer encapsulant, consisting of ≈ 300 CVD Si₃N₄ plus 600 evaporated AIN was also developed and found to withstand even higher temperatures (≈1150°C) and to provide more reliable and reproducible results than either AIN or Si₃N₄ when used singly. A double graphite strip heater was developed in order to improve the accuracy of annealing temperature and time measurements. This method was compared to existing annealing methods (single graphite strip, incoherent light and electron beam annealers) and was found superior in terms of temperature accuracy and reproducibility. A simple thermodynamic theory has been developed to explain the incorporation of Sn and Se implanted into GaAs using results obtained from a detailed study of electrical properties measured as a function of annealing temperature and time for 1 x 10¹⁴ cm-² dose implanted at an energy of 300 keV and RT. The electrical activity was found to increase with time and temperature but for sufficiently long times, this activity saturates for a given temperature. Detailed analysis of the data produced: i) an activation energy of 1.2 ± 0.1 eV which is suggested to be that required to remove Sn or Se from a complex defect where it is inactive or compensated and subsequently place it on an appropriate vacancy where it acts as a donor and, ii) activation energies of diffusion of 2.5 ± 0.1 eV and 4.3 ± 0.4 eVfor Sn and Se implants in GaAs, respectively.

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Code-barres	Cote	Support	Localisation	Section	Disponibilité	Spécialité	Etat_Exemplaire
D004086	D004086	Papier	Bibliothèque centrale	Thèse de Doctorat	Disponible

Documents numériques

BENSALEM.Rachid.pdf URL

Properties of silicon-on-insulator for bipolar integrated circuits / Azzedine Bellel 

Public ISBD Titre : Properties of silicon-on-insulator for bipolar integrated circuits Type de document : texte imprimé Auteurs : Azzedine Bellel, Auteur ; N. G. Emerson, Directeur de thèse Editeur : University of Surrey Année de publication : 1986 Importance : 93 f. Présentation : ill. Format : 30 cm. Note générale : Mémoire de Master : Electronique : Angleterre, University of Surrey : 1986 Bibliogr. f. 94 - 97 Langues : Anglais (eng) Mots-clés : Integrated  circuits Silicon  wafers Rutherford  backscattering Dielectric  isolation SOI  layers Index. décimale : Ms01286 Résumé : Silicon wafers have been implanted with 400 keV molecular oxygen, with a dose of 1.8 x 10¹⁸ O⁺/cm² at an implantation temperature of about 500°C. The wafers were annealed at 1200°C for 2 hours with SiO₂ cap. Rutherford backscattering has been used in the random mode to determine the thickness of the buried oxide. Leakage current through the oxide to the substrate or adjacent islands was measured. Dielectric isolation with leakage current of about 5 pA/mm² measured at 5V and breakdown field in excess of 7 MV/cm has been obtained, indicating that good island-to-substrate and island-to-island electrical isolation was achieved. Four point probe, Shockley-Haynes, and differential Hall techniques have been used to measure the electrical properties of the uppermost part of the SOI layers. For SOI substrates, the measured lifetimes are in the range 0.2 - 0.3 us, while for bulk silicon, the measured lifetimes are in the range 3 - 4 us. The relatively high lifetimes compared with SOS technology suggest the possibility of fabricating bipolar devices utilizing SOI structures. Minority as well as majority carrier mobilities obtained on SOI films are comparable with those of bulk silicon within the experimental uncertainty. The variation of the electrical resistivity for the SOI films with arsenic implant doses in the range 10¹² - 10¹⁵ As⁺/cm² has been shown to be similar to that in bulk silicon. The electrical profiles of the shallow electron distribution in the SOI substrates are comparable with that in the bulk silicon. All these results indicate that the uppermost part of the SOI layers are of comparable quality to bulk silicon. In this report, a comparative study of these electrical characteristics in SOI and bulk silicon is presented. Properties of silicon-on-insulator for bipolar integrated circuits [texte imprimé] / Azzedine Bellel, Auteur ; N. G. Emerson, Directeur de thèse . - [S.l.] : University of Surrey, 1986 . - 93 f. : ill. ; 30 cm. Mémoire de Master : Electronique : Angleterre, University of Surrey : 1986 Bibliogr. f. 94 - 97 Langues : Anglais (eng) Mots-clés : Integrated  circuits Silicon  wafers Rutherford  backscattering Dielectric  isolation SOI  layers Index. décimale : Ms01286 Résumé : Silicon wafers have been implanted with 400 keV molecular oxygen, with a dose of 1.8 x 10¹⁸ O⁺/cm² at an implantation temperature of about 500°C. The wafers were annealed at 1200°C for 2 hours with SiO₂ cap. Rutherford backscattering has been used in the random mode to determine the thickness of the buried oxide. Leakage current through the oxide to the substrate or adjacent islands was measured. Dielectric isolation with leakage current of about 5 pA/mm² measured at 5V and breakdown field in excess of 7 MV/cm has been obtained, indicating that good island-to-substrate and island-to-island electrical isolation was achieved. Four point probe, Shockley-Haynes, and differential Hall techniques have been used to measure the electrical properties of the uppermost part of the SOI layers. For SOI substrates, the measured lifetimes are in the range 0.2 - 0.3 us, while for bulk silicon, the measured lifetimes are in the range 3 - 4 us. The relatively high lifetimes compared with SOS technology suggest the possibility of fabricating bipolar devices utilizing SOI structures. Minority as well as majority carrier mobilities obtained on SOI films are comparable with those of bulk silicon within the experimental uncertainty. The variation of the electrical resistivity for the SOI films with arsenic implant doses in the range 10¹² - 10¹⁵ As⁺/cm² has been shown to be similar to that in bulk silicon. The electrical profiles of the shallow electron distribution in the SOI substrates are comparable with that in the bulk silicon. All these results indicate that the uppermost part of the SOI layers are of comparable quality to bulk silicon. In this report, a comparative study of these electrical characteristics in SOI and bulk silicon is presented.

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Code-barres	Cote	Support	Localisation	Section	Disponibilité	Spécialité	Etat_Exemplaire
Ms01286	Ms01286	Papier	Bibliothèque centrale	Mémoire de Master	Disponible

Documents numériques

BELLEL.Azzedine.pdf URL