Silicon-Based Integration of Groups III, IV, V Chemical Vapor Depositions in High-Quality Photodiodes

Heterogeneous integration of III-V semiconductors with silicon (Si) technology is an interesting approach to utilize the advantages of both high-speed photonic and electronic properties. The work presented in this thesis is initiated by this major goal of merging III-V semiconductor technology with Si technology. The focus was primitively placed on development of a Si-compatible tool for chemical vapor deposition (CVD) of gallium arsenide (GaAs). For this purpose, a Si/SiGe CVD reactor, ASMI Epsilon 2000, was extended with a TriMethylGallium (TMGa) bubbler system and extra tubing to allow the deposition of GaAs as well as the standard Si and SiGe depositions. Of key importance was to apply a very low arsine (AsH3) concentration: 0.7% as compared to the at least ten times higher values normally used in MOCVDs. The correspondingly low concentration of TMGa means that the contamination of the reactor chamber with gallium or arsenic is so low that standard high-quality low-doped Si and SiGe depositions can still be performed in the same CVD reactor chamber. In view of this, the research took a unique direction of creating devices where the merging of depositions of gallium (Ga), arsenic (As) and boron (B), together with Si and Ge, all in one reactor, proved indispensable. For the first time, deposition cycles containing layers of different combinations of these III, IV, V elements could then be performed without vacuum break. This was important not only for the growth of good quality GaAs epitaxy and crystalline Ge-on-Si, but also for the formation of junction diodes in these materials. In particular, the formation of p+n Si diodes of exceptional quality was facilitated by deposition of pure gallium (PureGa) or pure boron (PureB) to create the p+-region. The combination of both PureGa and PureB techniques have been implemented on crystalline Ge-on-Si to form ideal Ge-on-Si p+n junctions with world record low saturation currents. The term PureGaB is introduced for this technology. On the application side, this thesis work has been directed towards the very challenging feat of fabricating Ge avalanche photodiodes (Ge APDs)on Si substrates. The low dark current and clear breakdown curve of these diodes were proven to be suitable for infrared detection in linear and photon counting (Geiger) mode.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc

Large-area selective CVD epitaxial growth of Ge on Si substrates

Selective epitaxial growth of crystalline Ge on Si in a standard ASM Epsilon 2000 CVD reactor is investigated for the fabrication of Ge p+n diodes. At the deposition temperature of 700?C, most of the lattice mismatch-defects are trapped within first 300nm of Ge growth and good quality single crystal Ge is achieved within a layer thickness of approximately 1 ?m on window sizes up to hundreds of ?m2. For p+n junction fabrication, a sequence of pure-Ga and then pure-B depositions are utilized for the ultrashallow p-doping of As-doped Ge-islands. The I-V characterization of the diodes confirms the good quality of the Ge and ideality factors of ~ 1.1 with low saturation currents are reliably achievedDIMESElectrical Engineering, Mathematics and Computer Scienc

Ge-on-Si: Single-Crystal Selective Epitaxial Growth in a CVD reactor (abstract)

MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc

Ge-on-Si: Single-Crystal Selective Epitaxial Growth in a CVD Reactor

A standard Si/SiGe ASM CVD reactor that was recently modified for merging GaAs and Si epitaxial growth in one system is utilized to achieve intrinsic and doped epitaxial Ge-on-Si with low threading dislocation and defect densities. For this purpose, the system is equipped with 2% diluted GeH4 as the main precursor gas for Ge deposition; and 0.7% diluted AsH3 and B2H6 precursor gases as well as a TriMethylGallium (TMGa) bubbler system for As, B and Ga doping of epitaxial Ge, respectively. The quality of Ge epitaxy on Si is investigated by plan-view and cross-sectional transmission electron-microscopy (TEM) and atomic-force microscopy (AFM) analysis.Delft Institute of Microsystems and NanoelectronicsElectrical Engineering, Mathematics and Computer Scienc

Merging Standard CVD Techniques for GaAs and Si Epitaxial Growth

A commercial Chemical Vapor Deposition (CVD) system, the ASMI Epsilon 2000 designed for Si and SiGe epitaxy, has, for the first time, been equipped for the growth of GaAs compounds in a manner that does not exclude the use of the system also for Si-based depositions. With the new system, intrinsic, Si-doped and Ge-doped GaAs epitaxial layers with excellent quality have been grown on GaAs substrate wafers by the decomposition of trimethylgallium (TMGa) and AsH3 in the reactor at reduced pressure and at temperatures in the 600-700°C range. A low AsH3 concentration, 0.7 % in H2, is used as one of the precursors, which has the added advantage that the severe safety precautions always associated with MOCVD systems need not be implemented.Delft Institute of Microsystems and NanoelectronicsElectrical Engineering, Mathematics and Computer Scienc

CMOS-Compatible PureGaB Ge-on-Si APD pixel arrays

Pure gallium and pure boron (PureGaB) Ge-on-Si photodiodes were fabricated in a CMOS compatible process and operated in linear and avalanche mode. Three different pixel geometries with very different area-to-perimeter ratios were investigated in linear arrays of 300 pixels with each a size of 26 × 26 μm2. The processing of anode contacts at the anode perimeters leaving oxide covered PureGaB-only light-entrance windows, created perimeter defects that increased the vertical Ge volume but did not deteriorate the diode ideality. The dark current at 1 V reverse bias was below 35 μA/cm2 at room temperature and below the measurement limit of 2.5 × 10-2 μA/cm2 at 77 K. Spread in dark current levels and optical gain, that reached the range of 106 at 77 K, was lowest for the devices with largest perimeter. All device types were reliably operational in a wide temperature range from 77 K to room temperature. The spectral sensitivity of the detectors extended from visible to the telecom band with responsivities of 0.15 and 0.135 A/W at 850 and 940 nm, respectively.Electronic Components, Technology and Materials(OLD)Applied Quantum Architecture

Vanishing Zeeman energy in a two-dimensional hole gas

A clear signature of Zeeman split states crossing is observed in a Landau fan diagram of strained germanium two-dimensional hole gas. The underlying mechanisms are discussed based on a perturbative model yielding a closed formula for the critical magnetic fields. These fields depend strongly on the energy difference between the topmost and neighboring valence bands and are sensitive to the quantum well thickness, strain, and spin-orbit interaction. The latter is a necessary feature for the crossing to occur. This framework enables a straightforward quantification of the hole-state parameters from simple measurements, thus paving the way for its use in design and modeling of hole-based quantum devices.QCD/Scappucci LabQuTechBusiness Developmen

Integrated SiGe Detectors for Si Photonic Sensor Platforms

In this work, we present the results of integrated Ge detectors grown on a Si photonic platform for sensing applications. The detectors are fabricated on a passive photonic circuit for maximum coupling efficiency. Measurement results at 1300 nm wavelength show a responsivity of 0.2 A/W and very low dark current levels. For a voltage range between 0 and −10 V, the dark current is better than 0.1 nA which is crucial for highly sensitivity devices and applications, like OpticalCoherence Tomography.EKL ProcessingBusiness DevelopmentQuTechElectronic Components, Technology and Material

Single-hole pump in germanium

Single-charge pumps are the main candidates for quantum-based standards of the unit ampere because they can generate accurate and quantized electric currents. In order to approach the metrological requirements in terms of both accuracy and speed of operation, in the past decade there has been a focus on semiconductor-based devices. The use of a variety of semiconductor materials enables the universality of charge pump devices to be tested, a highly desirable demonstration for metrology, with GaAs and Si pumps at the forefront of these tests. Here, we show that pumping can be achieved in a yet unexplored semiconductor, i.e. germanium. We realise a single-hole pump with a tunable-barrier quantum dot electrostatically defined at a Ge/SiGe heterostructure interface. We observe quantized current plateaux by driving the system with a single sinusoidal drive up to a frequency of 100 MHz. The operation of the prototype was affected by accidental formation of multiple dots, probably due to disorder potential, and random charge fluctuations. We suggest straightforward refinements of the fabrication process to improve pump characteristics in future experiments 2021 The Author(s). Published by IOP Publishing Ltd.QCD/Veldhorst LabQuTechBUS/TNO STAFFQN/Veldhorst LabQCD/Scappucci La

A single-hole spin qubit

Qubits based on quantum dots have excellent prospects for scalable quantum technology due to their compatibility with standard semiconductor manufacturing. While early research focused on the simpler electron system, recent demonstrations using multi-hole quantum dots illustrated the favourable properties holes can offer for fast and scalable quantum control. Here, we establish a single-hole spin qubit in germanium and demonstrate the integration of single-shot readout and quantum control. We deplete a planar germanium double quantum dot to the last hole, confirmed by radio-frequency reflectrometry charge sensing. To demonstrate the integration of single-shot readout and qubit operation, we show Rabi driving on both qubits. We find remarkable electric control over the qubit resonance frequencies, providing great qubit addressability. Finally, we analyse the spin relaxation time, which we find to exceed one millisecond, setting the benchmark for hole quantum dot qubits. The ability to coherently manipulate a single hole spin underpins the quality of strained germanium and defines an excellent starting point for the construction of quantum hardware.QCD/Veldhorst LabBusiness DevelopmentQCD/Scappucci La