abstract: The first part of this dissertation reports the study of the vertical carrier transport and device application in InAs/InAs1-xSbx strain-balanced type-II superlattice. It is known that the low hole mobility in the InAs/InAs1-xSbx superlattice is considered as the main reason for the low internal quantum efficiency of its mid-wave and long-wave infrared photodetectors, compared with that of its HgCdTe counterparts. Optical measurements using time-resolved photoluminescence and steady-state photoluminescence spectroscopy are implemented to extract the diffusion coefficients and mobilities of holes in the superlattices at various temperatures from 12 K to 210 K. The sample structure consists of a mid-wave infrared superlattice absorber region grown atop a long-wave infrared superlattice probe region. An ambipolar diffusion model is adopted to extract the hole mobility. The results show that the hole mobility first increases from 0.2 cm2/Vs at 12 K and then levels off at ~50 cm2/Vs as the temperature exceeds ~60 K. An InAs/InAs1-xSbx type-II superlattice nBn long-wavelength barrier infrared photodetector has also been demonstrated with a measured dark current density of 9.5×10-4 A/cm2 and a maximum resistance-area product of 563 Ω-cm2 at 77 K under a bias of -0.5 V. The Arrhenius plot of the dark current density reveals a possible high-operating-temperature of 110 K.The second part of the dissertation reports a lift-off technology using a water-soluble sacrificial MgTe layer grown on InSb. This technique enables the seamless integration of materials with lattice constants near 6.5 Å, such as InSb, CdTe, PbTe, HgTe and Sn. Coherently strained MgTe with a lattice constant close to 6.5 Å acts as a sacrificial layer which reacts with water and releases the film above it. Freestanding CdTe/MgxCd1-xTe double-heterostructures resulting from the lift-off process show increased photoluminescence intensity due to enhanced extraction efficiency and photon-recycling effect. The lifted-off thin films show smooth and flat surfaces with 6.7 Å root-mean-square roughness revealed by atomic-force microscopy profiles. The increased photoluminescence intensity also confirms that the CdTe/MgxCd1-xTe double-heterostructures maintain the high optical quality after epitaxial lift-off. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2020

Cette thèse de doctorat traite de la mise en œuvre du procédé de soulèvement épitaxial (ou ELO pour epitaxial lift-off) à partir d'un substrat d'InP permettant le détachement des couches actives et le recyclage du substrat afin de rendre économiquement compétitive la fabrication de cellules solaires multi-jonctions pour le photovoltaïque concentré. Ce procédé, qui consiste à sous-graver sélectivement une couche sacrificielle comprise entre le substrat et les couches actives, est bien connu et maîtrisé sur un substrat de GaAs avec l'utilisation d'une couche sacrificielle d'AlAs d'épaisseur voisine de 5 nm, ce qui n'est pas possible sur un substrat d'InP en raison du fort désaccord de maille cristalline existant entre l'AlAs et l'InP. Pour l'adapter à un substrat d'InP, le développement d'une couche sacrificielle spécifique basée sur un super-réseau AlAs/InAlAs a été réalisé, ce qui permet de contourner les problématiques liées au désaccord de maille et à la croissance de matériaux contraints. Après optimisation des conditions de croissance de ce super-réseau, les épaisseurs atteintes et donc les vitesses de sous-gravure obtenues en utilisant ce type de couche sacrificielle ont satisfait aux exigences du procédé ELO. Ensuite, le report et le soulèvement de structures actives de cellules solaires InGaAs en couches minces cristallines ont été développés. Les cellules solaires ainsi fabriquées ont montré des performances semblables à celles réalisées par épitaxie standard sur un substrat d'InP, voire meilleures sous concentration en raison d'effets de confinement optique. Finalement, le recyclage du substrat d'InP réalisé avec un procédé utilisant seulement deux étapes de nettoyage par voies chimiques humides, a permis de produire des surfaces d'InP de qualité suffisante pour réaliser une reprise d'épitaxie satisfaisante. / This PhD thesis deals with the implementation of the epitaxial lift-off (ELO) process from an InP substrate allowing the detachment of active layers and the substrate recycling. The final target is to realize multi-junction solar cells in an economically competitive way for concentrated photovoltaic. The ELO process consists in the under-etching of a sacrificial layer inserted between the substrate and the active layers. It is well known and mastered on a GaAs substrate with the use of a sacrificial layer of AlAs with a thickness of about 5 nm. Such a layer is not usable on an InP substrate due to the high lattice mismatch between AlAs and InP. In order to adapt the ELO process to an InP substrate, this work aimed to develop a specific sacrificial layer based on an AlAs/InAlAs superlattice. Thus, it is possible to circumvent problems related to the lattice mismatch and to the strained layer growth. After optimization of growth conditions of this superlattice, using this type of sacrificial layer, we achieve a sufficient thickness and therefore a sufficient under-etching rate in order to meet the requirements of the ELO process. Then, the transfer and lift-off of thin crystalline film based InGaAs solar cells have been developed. This kind of solar cells showed performances similar to those obtained with a standard epitaxial growth on an InP substrate, or even better under concentration due to optical confinement effects. Finally, the recycling of the InP substrate carried out by a process using only two wet chemical cleaning steps made it possible to produce InP surfaces of sufficient quality to achieve a promising second epitaxial growth.