Project

Discipline

Unitraveling Carrier Photodiode; Sub-mm-waves; Photodiodes; THz Generation; High-Power Output; Millimeter-Wave Generation

Lead
LeadLes Photodiodes Unipolaires (Unitravaling Carrier Photodiodes, ou UTC-PDs) sont plus rapides que les diodes PIN traditionelles car elles n`impliquent pas le transport de porteurs de charges positives (trous). Cependant, pour obtenir une bonne puissance de sortie, les UTC-PDs traditionelles requièrent des gradation compositionelles qui augmentent la tension de claquage mais réduisent le courant maximal qui peut-être généré. Ce travail explorera l`utilisation du système GaAsSb-InP qui est libre des effets de blocage rencontrés dans les UTC-PDs traditionelles basées sur GaInAs.
Lay summary
Contenu et objectifs du travail de recherche De nouveaux alliages semiconducteurs seront explorés en visant une augmentation des largeurs de bande des UTC GaAsSb/InP en vue d`une éventuelle utilisation pour la génération de puissance à des fréquences de 200 à 400 GHz, voir jusqu`au régime THz. Contexte scientifique et social du projet de recherche Certains des alliages envisagés n`ont jamais été évalués pour les photodiodes UTC: une certaine avancée scientifique y est garantie. Pour les applications potentielles on peut envisager les communication optiques/sans fil à très haut débit (10-100 Gbs) et/ou la génération d`ondes THz pour applications telles que sécurité ou contrôle de la qualité durant la production de médicaments en industrie pharmaceutique. Keywords UTC-PD, MOCVD (metalorgfanic chemical vapor deposition), InP (Phosphure d`indium), GaAsSb (arsenure-antimoniure de gallium), photo-generation.

Direct link to Lay Summary

Last update: 11.10.2019

Number	Title	Start	Funding scheme

Unitraveling Carrier Photodiodes (UTC-PDs) provide improved photoresponses and bandwidths compared to conventional PIN photodiodes because UTC-PDs only rely on the motion of faster moving electrons through the photodiode depletion region by shifting light absorption to the p-contact region. The temporal response of the photogenerated slow-moving hole charge carriers corresponds to the dielectric relaxation time in the p-contact, and is short with respect to the electron transit time and diode RC time constant. The key remaining problem is then transferring the photo-generated electrons to a wider energy gap high-field drift collector.In conventional UTC-PDs on InP, photon absorption takes place in a p-type Ga0.47In0.53As layer: some form of compositional grading is required to ease electron transport from GaInAs to the InP drift collector (see Fig. 3 on p. 3 below). Under high optical excitation, the space charge of traveling electrons collapses the junction electric field and the photocurrent drops due to blocking associated with the (“Type-I”) band alignment between GaInAs and InP: even when grading is used, electrons experience an opposing quasi-electric field when bands are flattened by optical excitation. In contrast, a Ga(In)AsSb absorber with a “Type-II” (staggered) alignment to InP allows easy electron injection into InP even under zero-bias conditions. Theoretical computations at ETHZ, and simulations in the literature, show the “Type-II” system to be the optimal solution for the realization of high-output UTC-PDs. The PI`s Group has shown that InP/GaInAsSb Double Heterojunction Bipolar Transistors (DHBTs) feature higher fT cutoff frequencies than GaInAs-based DHBTs, demonstrating several advantages of the “Type-II” system which will carry over to the UTC-PD realization due to their physical commonalities with DHBTs.Significance: UTC-PDs are key enabling components in the photomixing generation of sub-mm wave to THz output with applications ranging from as >100 Gbit/s wireless communications to sensing/measurement in the health, pharmaceutical, scientific, and security domains (see Section 2.1b, p. 6). Considering the difficulty of generating signal power at sub-mm and THz frequencies, a fundamentally different UTC-PD relying on a favorable band alignment is a compelling and original alternative to fighting nature to transfer electrons from GaInAs to InP, as done in other approaches. From a purely scientific perspective, the proposed research will yield information on the physical properties of the little-studied GaInAsSb alloy grown lattice-matched to InP.Methods / Milestones / Output: Vertical absorption, top-illuminated Ga(In)AsSb/InP -based UTC-PDs will be grown by MOCVD and fabricated in the ETHZ FIRST Laboratory. The devices will be characterized by dark I-V measurements as well as for frequency response under various levels of optical excitation. The first objective is to demonstrate higher-power output and wider bandwidths than state-of-the-art results for comparatively-sized conventional “Type-I” GaInAs devices by properly designing the GaInAsSb absorber. Next, plasmonically-enhanced top contacts consisting of subwavelength grids or meshes/gratings will be exploited to maximize light absorption in thinner GaInAsSb absorber layers. Device performance will be characterized using lightwave analyzers up to 67 GHz in the applicant`s laboratory (for larger PDs), as well as by THz time domain spectroscopy (TDS) in one of several ETHZ TDS facilities to characterize the response of smaller area UTC-PDs (3-5 µm diameter) integrated with on-chip broadband antennae (bow-tie, log-periodic) well into the THz domain of frequencies.