Photon detectors based on single-crystalline materials are of great interest for high performance imaging applications due to their low noise and fast response. The major detector materials for sensing in the long-wavelength infrared (LWIR) band (8-14 µm) are currently HgCdTe (MCT) and AlGaAs/GaAs quantum wells (QW) used in intraband-based quantum-well infrared photodetectors (QWIPs). These either suffer from compositional variations that are detrimental to the system performance as in the case of MCT, or, have an efficient dark current generation mechanism that limits the operating temperature as for QWIPs. The need for increased on-wafer uniformity and elevated operating temperatures has resulted in the development of various alternative approaches, such as type-II strained-layer superlattice detectors (SLSs) and intraband quantum-dot infrared photodetectors (QDIPs).

In this work, we mainly explore two self-assembled quantum-dot (QD) materials for use as the absorber material in photon detectors for the LWIR, with the aim to develop low-dark current devices that can allow for high operating temperatures and high manufacturability. The detection mechanism is here based on type-II interband transitions from bound hole states in the QDs to continuum states in the matrix material.

Metal-organic vapor-phase epitaxy (MOVPE) was used to fabricate (Al)GaAs(Sb)/InAs and In(Ga)Sb/InAs QD structures for the development of an LWIR active material. A successive analysis of (Al)GaAs(Sb) QDs using absorption spectroscopy shows strong absorption in the range 6-12 µm interpreted to originate in intra-valence band transitions. Moreover, record-long photoluminescence (PL) wavelength up to 12 µm is demonstrated in InSb- and InGaSb QDs.

Mesa-etched single-pixel photodiodes were fabricated in which photoresponse is demonstrated up to 8 µm at 230 K with 10 In_0.5Ga_0.5Sb QD layers as the active region. The photoresponse is observed to be strongly temperature-dependent which is explained by hole trapping in the QDs. In the current design, the photoresponse is thermally limited at typical LWIR sensor operating temperatures (60-120 K), which is detrimental to the imaging performance. This can potentially be resolved by selecting a matrix material with a smaller barrier for thermionic emission of photo-excited holes. If such an arrangement can be achieved, type-II interband InGaSb QD structures can turn out to be interesting as a high-operating-temperature sensor material for thermal imaging applications.

The advancement of semiconductor optoelectronics relies extensively on materials and processing technologies of ever-increasing sophistication, such as nanometer-range lithography, epitaxial growth methods with monatomic layer control, and anisotropic etching procedures that allows for the precise sculpturing of device features even in the limit of extreme aspect ratios. However, upcoming application needs puts requirements on optimized designs or device performances, e.g. in terms of integration density, power efficiency, modulation bandwidth or spectral response, which call for innovative and refined methodologies. In the present thesis, we investigate a few different device designs or processing schemes that aims for extended performances or manufacturability as compared to presently available technologies. In specific, we study the design and fabrication of transistor-vertical-cavity surface-emitting lasers (T-VCSELs), the regrowth of InP-based driver electronics in the trenches of arrayed spatial light modulators (SLMs), the epitaxial growth and analysis of quantum dot (QD)-based interband photodetectors, the realization of InGaAs/GaAs QD-based single-photon emitters for the 1.55-μm waveband, as well as the fabrication of discrete and silicon-integrated photonic-crystal surface-emitting lasers (PCSELs).The transistor laser, invented at the University of Illinois around 2006, has received considerable interest due to potential major advantages in modulation bandwidth, noise properties and novel functionality as compared to conventional diode lasers. Here we study the design and fabrication of pnp-type 980-nm AlGaAs/InGaAs/GaAs T-VCSELs. Using an epitaxial regrowth process, an intracavity contacting scheme, and an optimized layer design, continuous-wave (CW) result in terms of threshold, output power and temperature performance comparable to conventional VCSELs could be demonstrated. In addition, the collector-current breakdown mechanism was shown to be due to a band-filling effect rather than an intracavity photon absorption process as previously suggested.A subsequent study regards the epitaxial regrowth for the integration of driver electronics with two-dimensional arrays of spatial light modulators (SLMs). The challenge here relies in controlling the regrowth morphology in the restricted areas that limit the SLM array fill factor. It is shown that the orientation of the SLM array with respect to the crystallographic directions is critical for controlling the regrowth7morphology, with mesa alignments along the <001> directions preferable over the <011> directions. Following this scheme, an optimized etch/regrowth process for top-contacted field-effect transistors is demonstrated.Next, we discuss the development of long-wavelength infrared (LWIR; 8-12 μm) detector elements for thermal imaging. Such detectors have traditionally been realized in the mercury-cadmium-telluride system (MCT; high performance but difficult materials properties resulting in high cost) or using AlGaAs/GaAs quantum-well infrared photodetectors (QWIPs; excellent manufacturing properties but compromised performance figures). In this work we consider interband QD photodetectors based on spatially indirect transitions in the In(Ga)Sb QD/InAs type-II system to combine the respective advantages of MCT detectors and QWIPs. An epitaxial growth process is optimized for photo-response in the LWIR regime, and the QD properties were also studied using excitation power-dependent PL and spatially resolved current-voltage spectroscopy using a scanning-tunneling microscope.Quantum dot-based structures were also studied for the development of single-photon telecommunication-wavelength emitters. In this case, InAs QDs were formed in an In-rich InGaAs metamorphic buffer layer grown on GaAs substrate. This resulted in narrow and bright micro-photoluminescence emission lines from isolated QDs around 1.55 μm at low temperature, thereby making the application of such QDs an interesting alternative approach to InAs/InP QDs for the realization of single-photon emitters for telecommunication-wavelength fiber-based quantum networks.Finally, we describe the development of silicon-integrated and discrete photonic-crystal surface-emitting lasers (PCSELs). In the former case, a transfer-print process is used to combine an SOI-based PC structure with an InP-based active region. This results in an ultra-shallow device structure and a buried tunnel-junction configuration is used for current injection. In the latter case, the metal-organic vapor-phase epitaxy (MOVPE) growth conditions are tuned to form perfectly encapsulated cavities in the InP matrix. Low-threshold lasing is thereby obtained from optical pumping.

Framstegen inom halvledarbaserad optoelektronik baseras i stor utsträckning på alltmer förfinad material och processteknologi, såsom litografi i nanometerskala, epitaxiala tillväxtmetoder med atomär skiktkontroll och starkt anisotropisk etsning av avancerade komponentstrukturer. Uppkommande applikationsbehov ställer emellertid allt större krav på optimerad design och komponentprestanda, t.ex. avseende integrationstäthet, energieffektivitet, modulationsbandbredd eller spektral respons, vilket kräver innovativa och förfinade metoder. I denna avhandling undersöks några olika komponentdesigner och tillverkningsmetoder som syftar till utökad prestanda och/eller tillverkningsförmåga jämfört med nu tillgänglig teknologi. Speciellt studeras design och tillverkning av transistor-vertikalkavitetslasrar (T-VCSELs), epitaxiell återodling av InP-baserad drivelektronik i pixelerade ljusmodulatorer (SLM), epitaxiell tillväxt och analys av kvantpricks (QD)-baserade interband-fotodetektorer, realisering av InGaAs/GaAs QD-baserade single-fotonsändare för telekommunikationsområdet, samt tillverkning av diskreta och kiselintegrerade fotonisk-kristall-baserade ytemitterande lasrar ( PCSEL).Transistorlasern, som uppfanns vid University of Illinois omkring 2006, har rönt stort intresse på grund av möjliga prestandafördelar relaterat till moduleringsbandbredd, brusegenskaper och ny funktionalitet jämfört med konventionella diodlasrar. Här studeras design och tillverkning av pnp-typ 980-nm AlGaAs/InGaAs/GaAs T-VCSEL. Med hjälp av en epitaxiell återodlingsprocess, intrakavitetskontakter och optimerad design, demonstreras T-VCSELs med continuous wave (CW)-resultat i termer av tröskel, uteffekt och temperaturprestanda jämförbara med konventionella VCSELs. Dessutom visas genombrottsmekanismen för kollektorström bero på en bandfyllnadseffekt snarare än en foton-assisterad absorptionsprocess som tidigare föreslagits.I ett annat sammanhang studeras epitaxial återodling för integration av drivelektronik i tvådimensionella pixelerade ljusmodulatorer (SLM). Utmaningen här består i att kontrollera återväxtmorfologin i de begränsade områdena som avskiljer SLM-pixlarna. Det visas att komponenternas orientering med avseende på de kristallografiska riktningarna är avgörande för att kontrollera9återodlingens morfologi. Det visas att en orientering av pixel-raderna längs <001>- snarare än <011> -riktningarna har en fördel i det sammanhanget. Baserat på dessa resultat utvecklas en etsnings/ återodlingsprocess för toppkontakterade fälteffekttransistorer.Därefter diskuteras utvecklingen av långvågiga infraröda (LWIR; 8-12 μm) detektorelement för värmekameror. Sådana detektorer har traditionellt realiserats i kvicksilver-kadmium-telluridsystemet (MCT; högpresterande men svåra materialegenskaper som resulterar i höga kostnader) eller med användning av AlGaAs/GaAs kvantbrunnsbaserad infraröda fotodetektorer (QWIPs; utmärkta tillverkningsegenskaper men mer modest prestanda). I detta arbete undersöks interband-QD-fotodetektorer baserade på rumsligt indirekta övergångar i In(Ga)Sb QD/InAs typ II-systemet för att kombinera prestanda och tillverkningsfördelarna i MCT- och QWIP-teknologierna. En epitaxiell tillväxtprocess optimerades för fotorespons i LWIR-området, och QD-egenskaperna studerades dessutom explicit med excitationsberoende PL och rumsligt upplöst tunnelspektroskopi med hjälp av ett sveptunnelmikroskop.Kvantprickbaserade strukturer studerades också för utveckling av singelfotonemittrar i telekommunikationvåglängdsområdet. I detta fall bildades InAs kvantprickar i ett In-rikt InGaAs metamorfiskt buffertlager odlat på ett GaAs-substrat. Detta resulterade i smala och ljusstarka fotoluminiscensinjer från isolerade kvantprickar vid en vågländ runt 1,55 μm vid låg temperatur. Detta gör tillämpningen av sådana kvantprickar till ett intressant alternativt till InAs/InP kvantprickar för realisering av singelfotonemittrar för telekomvåglängdsbaserade kvantnätverk.Slutligen beskrivs utvecklingen av kiselintegrerade samt diskreta fotonisk-kristall-baserade ytemitterande lasrar (PCSELs). I det förra fallet används en transfer-print-process för att kombinera en SOI-baserad fotonisk-kristall-struktur med InP-baserade aktivt material. Detta resulterar i en extremt kompakt komponentstruktur där en begravd tunneldiod används för ströminjektion. I det senare fallet justeras tillväxtparametrarna i MOVPE-processen för skapa en fotonisk-kristall-struktur med luft-fyllda håligheter i InP-materialet. Lasring uppvisades genom optisk pumpning.