Ze Yuan

Strained germanium thin film membrane on silicon substrate for optoelectronics

This work presents a novel method to introduce a sustainable biaxial tensile strain larger than 1% in a thin Ge membrane using a stressor layer integrated on a Si substrate. Raman spectroscopy confirms 1.13% strain and photoluminescence shows a direct band gap reduction of 100meV with enhanced light emission efficiency. Simulation results predict that a combination of 1.1% strain and heavy n(+) doping reduces the required injected carrier density for population inversion by over a factor of 60. We also present the first highly strained Ge photodetector, showing an excellent responsivity well beyond 1.6um.

Roadmap to an Efficient Germanium-on-Silicon Laser: Strain vs. n-Type Doping

We provide a theoretical analysis of the relative merits of tensile strain and n-type doping as approaches to realizing an efficient low-power germanium laser. Ultimately, tensile strain offers threshold reductions of over 200x, and significant improvements in slope efficiency compared with the recently demonstrated 0.25% strained electrically pumped germanium laser. In contrast, doping offers fundamentally limited benefits, and too much doping is harmful. Moreover, we predict that tensile strain reduces the optimal doping value and that experimentally demonstrated doping has already reached its fundamental limit. We therefore theoretically show large (>; 1%) tensile strain to be the most viable path to a practical germanium-on-silicon laser.

Optimization of the

While there have been many demonstrations on n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) in III-V semiconductors showing excellent electron mobility and high drive currents, hole mobility in III-V p-channel MOSFETs (pMOSFETs) has traditionally lagged in comparison to silicon. GaSb is an attractive candidate for high-performance III-V pMOSFETs due to its high bulk hole mobility. We fabricate and study GaSb pMOSFETs with an atomic layer deposition Al₂O₃ gate dielectric and a self-aligned source/drain formed by ion implantation. The band offsets of Al₂O₃ on GaSb were measured using synchrotron radiation photoemission spectroscopy. The use of a forming gas anneal to passivate the dangling bonds in the bulk of the dielectric was demonstrated. The density of interface states <i>D</i>_it was measured across the GaSb band gap using conductance measurements, and a midband-gap <i>D</i>_it of 3 × 10¹¹/cm² eV was achieved. This enabled pMOSFETs with a peak hole mobility value of 290 cm²/Vs.

\hbox{Al}_{2}\hbox{O}_{3}/ \hbox{GaSb}

We have studied the surface cleaning of Sb-based compound semiconductors using HF, NH4OH, and HCl cleans and the metal–oxide–semiconductor (MOS) capacitors fabricated subsequently. GaSb, InGaSb, and AlGaSb surfaces are investigated using low-energy radiation from the synchrotron. Capacitance–voltage (C–V) and photoluminescence measurements are carried out on capacitors made with Al2O3 from atomic layer deposition and corroborated with the results from synchrotron spectroscopy. Excellent C–V characteristics with a mid-band-gap interface state density of 3 × 1011/cm2eV are obtained on samples with the HCl clean. This is consistent with the finding that only the HCl acid clean is able to remove the native oxides present on GaSb and InGaSb surfaces, and produce clean and stable surfaces suitable for MOSFET development. Complete removal of AlOx on the AlGaSb surface was not possible using chemical cleaning. Termination of AlGaSb with two monolayers of GaSb is proposed as a solution.

Interface and a High-Mobility GaSb pMOSFET

InxGa1-xSb is an attractive candidate for high performance III-V p-metal-oxide-semiconductor field effect transistors (pMOSFETs) due to its high bulk hole mobility that can be further enhanced with the use of strain. We fabricate and study InxGa1−xSb-channel pMOSFETs with atomic layer deposition Al2O3 dielectric and self-aligned source/drain formed by ion implantation. The effects of strain and heterostructure design for enhancing transistor performance are studied systematically. Different amounts of biaxial compression are introduced during MBE growth, and the effect of uniaxial strain is studied using wafer-bending experiments. Both surface and buried channel MOSFET designs are investigated. Buried (surface) channel InxGa1−xSb pMOSFETs with peak hole mobility of 910 (620) cm2/Vs and subthreshold swing of 120 mV/decade are demonstrated. Pulsed I-V measurements and low-temperature I-V measurements are used to investigate the physics in transistor characteristics.

Device quality Sb-based compound semiconductor surface: A comparative study of chemical cleaning

In<inf>x</inf>Ga<inf>1−x</inf>Sb pMOSFETs with SS of 120mV/decade, I<inf>ON</inf>/I<inf>OFF</inf>>10⁴ and Gm,max of 140/90 mS/mm (L<inf>G</inf>=5µm), fabricated using a self-aligned gate-first process are demonstrated for the first time. Table 2, summarizes the key transistor results. ALD Al<inf>2</inf>O<inf>3</inf> with Dit of 3×10¹¹/cm²eV and strain engineering has enabled a high-mobility In<inf>x</inf>Ga<inf>1−x</inf>Sb pMOSFET an important step toward the implementation of III–V CMOS in future technology nodes.

InxGa1-xSb channel p-metal-oxide-semiconductor field effect transistors: Effect of strain and heterostructure design

Fermi level pinning near GaSb valence band edge leads to high Schottky barrier height for metal/n-type GaSb contacts. However, this effect can be alleviated by depinning of the Fermi level with the introduction of thin interfacial dielectric. In this paper, the use of TiO2 allows depinning of the Fermi level without introducing excessive tunneling resistance due to the low conduction band offset, estimated by synchrotron radiation photoemission spectroscopy. It is shown the insertion of TiO2 results in reduction in Schottky barrier height and greater than four orders of magnitude increase in current density for metal contacts on n-type GaSb.

Development of high-k dielectric for antimonides and a sub 350°C III–V pMOSFET outperforming Germanium

In this letter, we study the formation and electrical properties of Ni-GaSb alloys by direct reaction of Ni with GaSb. It is found that several properties of Ni-antimonide alloys, including low thermal budget processing (300°C), low Schottky barrier height for holes (~0.1 eV), low sheet resistance of Ni-InGaSb (53 Ω/\square), and low specific contact resistivity (7.6×10)^-7Ω cm²), show good progress toward antimonide-based metal source/drain (S/D) p-channel metal-oxide-semiconductor field-effect transistors. Devices with a self-aligned metal S/D were demonstrated, in which heterostructure design is adopted to further improve the performance, e.g., ON/OFF ratio , subthreshold swing (140 mV/decade), and high effective-field hole mobility of ~510 cm²/Vs at sheet charge density of 2×10¹² cm^-2.

Schottky barrier height reduction for metal/n-GaSb contact by inserting TiO2 interfacial layer with low tunneling resistance

There has been an upsurge of interest in the possibility of a low-power, high-performance CMOS based on III-V materials. For such a technology to be realized, advances are needed in a number of areas including: (a) comparable high performance from n- and p-channel devices for complementary logic; (b) reducing the impact of Dit; and (c) overcoming low density of states (DOS) of electrons which could limit the NMOS ION. In this study, methods are investigated that deliver improvements in these three areas (Fig. 1). We chose to work on the 6.1-6.2Å lattice constant system with InGaSb as the channel material because of its advantages in terms of band engineering and high mobility/offsets for both electrons and holes [1-2]. Despite its larger lattice constant, antimonides are also found to be potentially more suitable for hetero-integration [3]. We demonstrate electron/hole mobility >; 4000/900cm2/Vs can be achieved in a single channel material. For the first time in III-V systems, both n- and p-channel transistors with one single channel material show comparable high on-current.

Antimonide-Based Heterostructure p-Channel MOSFETs With Ni-Alloy Source/Drain

Performance degradation due to interfacial traps is generally considered as one of the main challenges for III-V metal-oxide-semiconductor field-effect-transistors (MOSFETs). In this work, we have investigated the suppression of interface state response using band engineering in III-V quantum well MOSFETs and experimentally verified the concept in the antimonide materials system using a gate-stack consisting of Al2O3/GaSb/InAlSb. It is shown that if the thickness of the interfacial layer of GaSb is scaled down to a few monolayers, the effective bandgap of the interfacial layer increases dramatically due to quantum confinement, which leads to the suppression of interface-trap response.