InAs/GaSb superlattices are a material system well suited to growth via molecular beam epitaxy. The ability to tune the band gap over the entire mid and long wave infrared spectrum gives a large number of applications for devices made from InAs/GaSb superlattice material. The growth of high quality InAs/GaSb superlattice material requires a careful study of the parameters used during epitaxial growth. This work investigates the growth of tunnel junctions for InAs/GaSb based superlattice light emitting diodes, the presence of defects in GaSb homoepitaxial layers, and variations in the growth rate of InAs/GaSb superlattice samples. Tunnel junctions in cascaded structures must provide adequate barriers to prevent carriers from leaking from one emission region to the next without first recombining radiatively, while at the same time remain low in tunneling resistance for current recycling. A variety of tunnel junction designs are compared in otherwise identical four stage InAs/GaSb superlattice light emitting diodes, which past studies have found hole confinement to be problematic. GaSb was used on the p-side of the junction, while various materials were used on the n-side. Al0.20In0.80As0.73Sb0.27 tunnel junctions function best due to the combination of favorable band alignment and ease of growth. Pyramidal defects have been observed in layers of GaSb grown by molecular beam epitaxy on GaSb substrates. These defects are typically 3-8 nanometers high, 1-3 microns in diameter, and shaped like pyramids. Their occurrence in the growth of GaSb buffer layers can propagate into subsequent layers. Defects are nucleated during the early stages of growth after the thermal desorption of native oxide from the GaSb substrate. These defects grow into pyramids due to a repulsive Ehrlich-Schwoebel potential on atomic step edges leading to an upward adatom current. The defects reduce in density with growth of GaSb. The insertion of a thin AlAsSb layer into the early stages of the GaSb buffer increases the rate of elimination of the defects, resulting in a smooth surface within 500nm. The acceleration of defect reduction is due to the temporary interruption of step-flow growth induced by the AlAsSb layer. This leads to a reduced isolation of the pyramids from the GaSb epitaxial layer, and allows the pyramidal defects to smooth out. Investigations into varying the superlattice growth rate have not been reported widely in the literature. Due to the frequent use of soaks, growth interrupts, and other interface structuring steps the superlattice growth rate and the interface layer sequence are linked. In order to properly study the effects of growth rate variations and interface design changes it is necessary to account for the effect on growth rate due to the interfaces. To this end it is useful to think of the effective growth rate of the superlattice, which is the total layer thickness divided by the total time, per superlattice period. Varying the effective growth rate of superlattice photoluminescence samples shows a peak in output at ˜ 0.5 monolayers per second. Investigations into the structural properties of the superlattices show no decrease in structural uniformity for effective growth rates up to ˜ 1.4 monolayers per second.

This dissertation contains two parts which is included the Gallium antimony (GaSb) thin film and quantum dots grown by ALE-MBE process. The ALE-MBE technology was used to get better film quality and to control exactly the thickness of epitaxial layers for quantum dots growth. For the larger lattice mismatch, it will be carefully controlled the substrate temperature and V/III flux ratio based on the growth mechanism to obtain the high quality of GaSb films. After fully understanding the GaSb films growth, the characteristics of GaSb quantum dots such as the density and size could be controlled. The XRD, Raman and Photo-reflectance measurements were used for obtaining the optimum growth conditions of Gasb films shown at temperature; 500~520¢Jand the V/III flux ratio about 2.5~3. The formation of three dimensional GaSb islands on GaAs substrate is expected at the deposition of a critical number of GaSb monolayer, About 3.1 monolayer grown is the optimum growth condition, and samples were characterized by atomic force microscopy (AFM). In order to control the dots size, sharp and dots density, the growth mechanism were discussed by analyzing different growth parameters included the growth temperature, thickness of monolayer, growth interruption time (GRI), and capped layer in detail.

Any object can emit infrared radiation if their temperature higher than 0K.Because of this,the photodetectors for infrared radition is very important in application. First,this paper will introduce the kinds and properties of infrared photodetectors but most important is the quantum dot infrared photodetectors.In second chapter,we use the basic physic concepts and mathematical equations to infer the photocurrent and dark current formula. According to the formula,we can see the relationship between current and quantum dot density,bias,donorconcentration, Temperature. After we get the relationship,we can discuss the detectivity,noise properties, optical gain responstivity, differential photoconductivity. According to our research,the electron will be heated at very high ,bias and make the photoconductivity fairly smooth.Moreover,an increase in the effective temperature can result in the occurrence of the voltage range,where differential photoconductivity, is negative. It is important for a infrared photodetector to have high responsivity,detectivity,high working temperature,low dark current and low noise.Excepting this,to comprise a best infrared photodetector must have a good control on growth condition. Because of this,this paper will discuss the relationship between quantum dot and temperature,GRI time, growth thickness,deposited QD material.Finally,this paper find the best growth condition to form a quantum dot infrared photodetector.

GaSb Thermophotovoltaics are a key technology in the search for the ability to power small scale autonomous systems. In this work, MBE grown GaSb photovoltaic devices are fabricated and tested under AM 1.5 conditions. These devices displayed short circuit current values as high as 40 mA/cm2 but were found to have poor series resistance. The parasitic resistive characteristics were factored out of the measured cell data and it was found that the photocurrent for the fabricated devices could be as much as 6 mA/cm2 higher then the measured short circuit current. An additional layer of metal was added to the reduce the deleterious resistance characteristics, and it was found to lower the series resistance down to a 4 Ω average across almost all of the devices. The average JSC for all of these devices increased to over 30 mA/cm2, with highs well over 40 mA/cm2, a more consistent result than the original single metal deposition devices. Graphene was applied to the originally fabricated devices in an attempt to remove the series resistances issues as well as act as a surface passivation layer. The graphene was able to reduce series resistance by as much as 50% on some of the devices, with a corresponding 6 mA/cm2 increase in short circuit current exhibited. The photocurrent and diode current values were not changed by more than a measurement error, an indication that surface passivaiton may not have taken place. Graphene was a suitable approach for solving the series resistance issue and its use as both a transparent conductive layer and surface passivation material deserve further investigation. / Master of Science

Le transfert des données est le principal défi pour répondre à la demande croissante d’échange d’informations au 21eme siècle. Une amélioration possible des dispositifs actuels réside dans le passage vers une technologie d’interconnexions optiques. Cette thèse explore le développement de lasers à semi-conducteurs III-V à base de GaSb (III-Sb) épitaxiés par jets moléculaires (EJM) pour obtenir des sources laser émettant vers 1,55 µm, la gamme des télécommunications, et leur intégration sur substrat Si. Les III-Sb présentent des propriétés intéressantes en termes de relaxation des contraintes, mais sont plutôt adaptés pour une émission dans le moyen – infrarouge. Grâce à un nouveau dessin de zone active basé sur l’insertion de plans atomiques d’Al0.68In0.32Sb dans des puits quantiques Ga0.8In0 .2Sb nous avons obtenu par technologie en voie humide à l'Université de Montpellier des lasers GaSb fonctionnant en continu à température ambiante à 1,55 µm avec des performances comparables à l’état de l’art dans ce domaine. Par la suite, j'ai développé et optimisé au III – V Lab et à l’Université de Montpellier deux technologies basées sur la gravure sèche des structures. Cela a permis de réduire la largeur du ruban laser jusqu’à 1,5 µm, ce qui d’après mes simulations est nécessaire pour obtenir un fonctionnement monomode transverse du laser indispensable pour les applications en télécommunications. Nous avons également étudié la croissance EJM des III-Sb sur substrat Si pour intégrer directement les lasers sur ce substrat. Nous avons obtenu les premiers lasers GaSb intégrés sur Si fonctionnant en continu à température ambiante vers 1.55 µm. Pour un composant de 1 mm x 10 µm, le courant de seuil est de 300 mA et la puissance optique par facette non-traitée est de 3,2 mW à 500 mA de courant injecté. Ces résultats ouvrent la voie à l’intégration monolithique de lasers III-Sb sur plateformes Si pour des applications télécom. / The transfer of information is the main challenge to meet the growing demand of IT capacities in the 21st century. A possible improvement of existing devices is shifting to optical interconnects technology.This PhD explores the molecular-beam epitaxy (MBE) growth and development of antimonide (III-Sb) III-V semiconductor lasers for emission in the telecom range, near 1.55 µm, and their integration on Silicon substrates. III-Sb present interesting properties in term of strain relaxation but they are characterized by a natural emission in the mid – infrared range. Thanks to a new active zone design based on inserting monolayer-thin Al0.68In0.32Sb layers inside Ga0.8InSb QWs, we have obtained by wet processing at Université de Montpellier GaSb-based lasers working in continuous wave above room temperature, at the target wavelength. In addition, their performances were comparable to the performances of the well – established InP technology used in commercial telecom devices. Next, I have developed and optimized at both III-V Lab and Université de Montpellier new process flows based on dry etching of the structures. This allowed reducing the laser ridge width down to 1.5 µm, a value that modeling shows to be needed for single transverse-mode operation. In addition, we have investigated the MBE growth of III-Sb on Si substrates for the direct integration of lasers. We demonstrated the first cw, room temperature laser emission near 1.55 µm from GaSb devices integrated onto Si. For a 1 mm x 10µm diodes the threshold current was of 300 mA and the optical power per uncoated facet was 3.2 mW under 500 mA injected current. These results open the way to the monolithic integration on Si platforms of III-Sb devices for telecom applications.

This study presents the GaSb epitaxial grown by molecular beam epitaxy (MBE) on the semi-insulating GaAs substrate and n+-GaAs substrate. Investigations are made to the effect of Sb4/Ga beam equivalent pressure (BEP) ratios on the current-voltage characteristics of the p-n hetero-junction and the metal-GaSb semiconductor Schottky contact for various metals deposited on n-type GaSb layers. Several growth conditions were taken to improve the quality of GaSb epitaxial films. The structure of GaSb epitaxial layers are characterized by the X-ray diffraction, and the optimum growth conditions 500¢J of substrate temperature and the Sb4/Ga flux ratio about 2~3 have been obtained. From the I-V curve of GaSb Schottky diodes, we know that the higher Sb4/Ga ratio will induce the lower breakdown voltage. Hence, the interface properties of hetero-junction between the GaSb/GaAs and metal/GaSb can be investigated by the current-voltage characteristics, in which the current leakages and the surface state density are strongly dependent on the ratio of Sb4/Ga BEP. Based on the thermionic emission theory, the barrier height obtained was decrease with the Sb4/Ga ratio increases. After metal deposited on the GaSb epitaxial film to form the Schottky diode, the density of surface states can be calculated from the relationship of metal work-function and barrier height, which were obtained from the current-voltage characteristics of Schottky diode measurement, and then it also found that the density of surface states show decrease as the Sb4/Ga ratio increase.

MBE ( Molecular Beam Epitaxy ) technique can obtain high quality of GaSb/GaAs hetero-junction structure and control epilayers precisely.It has 7¢Mlattice mismatch between GaAs ( substrate ) and GaSb ( thin film ), but if we control beam flux ratio (V/III) and substrate temperature exactly, we can obtain high quality of epilayer. The growth mechanisms related to the major factors of (1) Beam flux ratio (V/III)¡B(2) Substrate temperature. The properties of GaSb epilayers are characterized by different methods such as the X-ray diffraction. The optimum growth conditions 500¢J of substrate temperature and the V/III flux ratio about 2.5 have been obtained. On the basis of this condition, We use simulation program for solar cell ( Scaps ), to simulate GaSb/GaAs hetero-junction solar cell structure, to try the possibility of the GaSb/GaAs hetero-junction structure in solar cells. From the simulation result, we know if the doped concentration in the two semiconductor materials and thickness are suitability, and if we can control the concentration of interface states under a suitable value, the efficiency of the solar cell can well. On the basis of this result, the same for thermo-photovoltaic (TPV), its' efficiency will also well.

GaSb is a semiconductor material having a narrow band gap in the infrared spectrum of 0.72 eV. This research is intended to investigate the low cost growth and properties of GaSb and to propose this material as a candidate for a cost effective method of developing a GaSb /silicon tandem solar cell. This work investigated the sputtering of GaSb films onto a glass substrate from a GaSb/Sb split-sputtering target. A GaSb compound was formed by placing Ga and Sb elements inside a vacuum sealed ampule. The ampule was placed inside a box furnace and heated at 800 0 C successfully forming a GaSb compound. Both GaSb and Sb were molded into a semicircular shape in a quartz container. X-ray diffraction (XRD) was conducted on sputtered films in order to confirm their structure. XRD peaks of the film were compared with reference peaks found on the Inorganic Crystal Structure Database (ICSD). GaSb peaks were apparent at specific sputtering chamber conditions of substrate temperature and source-to-substrate distance. Sputtered GaSb films were then further characterized with the Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Hall Effect measurements. A theoretical thickness of the films was calculated using FTIR measurements to be about 1 μm and 0.35 μm for the films grown on a substrate heated with heater powers of 280 watts and 250 watts respectively. SEM confirmed the sample thicknesses with 20% error. Hall Effect measurements resulted in a high carrier concentration and low free carrier activation energy; 7.545 x1019 cm-3 and 0.1017 eV respectively. These values are attributed to the possible existence of anti-site defects. / Thesis / Master of Applied Science (MASc)

Gallium antimonide (GaSb) is a promising low-bandgap binary substrate for the fabrication of various infrared-based optoelectronic devices, particularly thermophotovoltaics (TPV). In order to make GaSb-based technologies like TPV more widely available, non-epitaxial dop- ing methods for GaSb must be pursued. Ion implantation is relatively unexplored for GaSb, and can offer advantages over the more common method of zinc diffusion, including higher flexibility with regards to substrate type and control over the resulting doping profile. Pre- vious work has shown beryllium (Be+) implantation to be a suitable method for fabricating a diode in an n-type GaSb substrate, opening the possibility for other ions to be considered for implanting into both n-type and p-type substrates. This work identifies sulfur (S+) as another species to investigate for this purpose. To do so, material and electrical characterization was done on S+ and beryllium implanted GaSb films grown onto a semi-insulating gallium arsenide (GaAs) substrate. X-ray Diffraction spectroscopy (XRD) and Atomic Force Microscopy (AFM) indicate that the post-implant anneal of 600 for 10 s repaired the implant damage in the bulk material, but left behind a damaged surface layer composed of coalesced vacancies. While the beryllium implant resulted in moderate doping concentrations corresponding to an activation percentage near 15 %, Hall Effect data showed that implanting S+ ions induced a strongly p-type behavior, with hole concentrations above 1 × 19 cm^3 and sheet hole densities 3.5 times higher than the total implanted dose. This strong p-type behavior is attributed to the remaining lattice damage caused by the implant, which induces a large density of acceptor-like defect states near the valence band edge. This technique was used on an unintentionally-doped p-type GaSb substrate to create a + /p junction. The implant process succeeded in producing a potential barrier similar to that of a hole-majority camel diode with a thin delta-doped region suitable for collecting diffused carriers from the p-type substrate. A post-fabrication etching process had the effect of strongly increasing the short circuit current density to as high as 41.8 mA/cm^2 and the open circuit voltage as high as 0.21 V by simultaneously removing a high carrier recombination surface layer. This etching process resulted in a broadband spectral response, giving internal quantum efficiencies greater than 90 %. / Doctor of Philosophy / Thermophotovoltaics (TPV) is a technology that converts light and other forms of electromagnetic energy into electrical power, much like a typical solar panel. However, instead of sunlight, the energy source used in a TPV system is a terrestrial heat source at a temperature range of 1250–1750 ◦C, whose radiation is primarily infrared (IR). The IR-absorbing qualities and commercial availability of the compound semiconductor gallium antimonide (GaSb) have made it a key component in the development of absorber devices for TPV-related systems. GaSb-based devices have most often been fabricated using epitaxy, a method in which layer(s) of material are ‘grown’ in a layer-by-layer fashion atop a substrate GaSb wafer to induce an interface between negatively-charged (n-type) and positively-charged (p-type) regions. In order to improve upon the scalability of TPV production, device fabrication methods for GaSb that avoid the use of epitaxy are sought after as a lower-cost alternative. In this work, sulfur ion implantation is examined as one of these methods, in which elemental sulfur ions are injected at a high energy into a p-type GaSb substrate. The implanted ions then alter the charge characteristics at the surface of the material, producing an electric field from which a photovoltaic (PV) device can be fabricated. The results of this study showed that by implanting sulfur ions, an extremely p-type (p++) layer was formed at the surface of the GaSb substrate, which was attributed to residual damage induced by the implant process. The resulting interface between the p++ surface and the moderately p-type GaSb substrate was found to induce an electric field suitable for a PV device. Removing the excess surface damage away from the device’s metal contacts resulted in an improvement in the output electrical currents, with measured values being significantly higher than that of other devices made using more common non-epitaxial fabrication methods. The success of this work demonstrates the advantages of using a p-type GaSb substrate in place of an n-type substrate, and could help diversify the types of TPV-related devices that can be produced.

III-V compound Gallium Antimonide (GaSb), with a low bandgap of 0.72 eV at room temperature, is an attractive candidate for a variety of potential applications in optoelectronic devices. Ion implantation, among non-epitaxial methods, is a common and reliable doping technique to achieve local doping and obtain high-performance ohmic contacts in order to form a pn junction in such devices. An advantage of this technique over the diffusion method is the ability to perform a low-temperature process leading to accurate control of the dopant profile and avoiding Sb evaporation from GaSb surface occurring at 370 C. In this work, the effect of protons and sulfur ions as two implant species on the electrical behavior of MBE-grown undoped GaSb on semi-insulating (SI) GaAs was investigated via the Hall Effect. Protons and sulfur ions were implanted at room temperature (27 C) and 200 C, respectively, and rapid thermal annealing (RTA) was implemented at various temperatures and durations upon encapsulated GaSb. The damage induced by protons enhanced the hole density of GaSb up to around 10 times, whereas mobilities showed both increase and decrease compared to the un-implanted one, depending on the dose. While the activation of sulfur donors at an elevated temperature was anticipated after annealing sulfur implanted GaSb, instead it led to increase in p-type concentration, as the residual damage originated from sulfur implantation dominated substitutional doping. Furthermore, GaSb p/n photovoltaic devices were fabricated by applying sulfur implantation through silicon nitride layer at RT into an n-GaSb wafer (n-type base, p-type emitter). The device showed a rectifying current and photovoltaic characteristic. The J-V plot under AM1.5G illumination conditions, before and after an etch-back optimizing process, indicated lower short circuit current density J_sc, the same open circuit voltage V_oc, and higher fill factor FF, compared to the photovoltaic device with a p-type base. Also, both normalized series R_s and shunt R_p resistances in p/n diode indicated lower and higher values, respectively, as opposed to a GaSb p++/p diode, indicative of higher quality and lower manufacturing defects. / Master of Science / Generally, the photovoltaic effect is a process by which voltage or electric current is generated in a photovoltaic cell when exposed to light. A solar cell is a photovoltaic device, typically consisting a pn junction, that converts incident photon power into electrical power and delivered to a load to do electrical work for variety of applications. There are variety of methods to form a pn junction and fabricate such devices, among which ion implantation is a reliable doping technique. In this process, dopant ions are accelerated and smashed into a perfect semiconductor lattice, creating a cascade of damage that may displace a thousand atoms for each implanted ion and become activated after an annealing process. The ions themselves can act as either electron donors, make the semiconductor n-type, or electron acceptors, make it p-type. In this work, sulfur ions and protons, as two implant species, were implanted into separate Gallium Antimonide (GaSb) substrates and the effect of each on the electrical behavior of GaSb was investigated by Hall effect experiment. Both species raised hole carrier concentration. This behavior was not expected for sulfur ions as they would be assumed to act as electron donors after activation and convert the GaSb surface to an n-type semiconductor. It was identified that this behavior is due to the domination of created defects during implantation over the number of activated sulfur donors. The same characteristics were predicted and verified for proton implantation as well, the effect of which is just leaving damage in the lattice. Furthermore, to verify this method for converting n-type GaSb to p-type and fabricating a pn junction in GaSb for photovoltaic application, sulfur implantation into an n-type GaSb wafer was performed and optimized by removing the excess surface damage away from the device's metal contacts using wet etching. The device showed a diode-like rectifying current and photovoltaic characteristic. Some parameters such as short circuit current density J_sc, open circuit voltage V_oc, fill factor FF, and resistances (shunt and series) were measured and calculated using J-V plot under dark and illuminated conditions.