A. Karmous

Energy-Band Engineering for Improved Charge Retention in Fully Self-Aligned Double Floating-Gate Single-Electron Memories

We present a new fully self-aligned single-electron memory with a single pair of nano floating gates, made of different materials (Si and Ge). The energy barrier that prevents stored charge leakage is induced not only by quantum effects but also by the conduction-band offset that arises between Ge and Si. The dimensions and position of each floating gate are well-defined and controlled. The devices exhibit a long retention time and single-electron injection at room temperature.

Ge quantum dot tunneling diode with room temperature negative differential resistance

We present current density-voltage characteristics of Ge quantum dot p+-i-n+ tunneling diodes. The diode structure with Ge quantum dots embedded in the intrinsic region was grown by low temperature molecular beam epitaxy without any postgrowth annealing steps. The quantum dot diodes were fabricated using a low thermal budget fabrication process which preserves the Ge quantum structure. A negative differential resistance at room temperature of a Ge quantum dot tunneling diode was observed. A maximum peak to valley ratio of 1.6 at room temperature was achieved.

Integrated W-band RECTENNA (rectifying antenna) with Ge quantum dot Schottky Diode

In this paper we will present our latest research results of the integrated RECTENNA (the rectifying antenna) with a THz quantum dot Schottky Diode and an integrated silicon antenna for RF applications. Within this work a specific antenna design, an integrated single patch antenna, will be shown. A layer of Ge quantum dot (QD) was embedded in an integrated Si Schottky barrier diode. The high frequency limit 1.1THz was calculated from S-parameter measurements up to 110GHz. Both are integrated on HR-Si substrates forming a simple mm-wave power detection system. First RF measurement results of RECTENNA up to 110GHz are shown.

Integrated Quantum Dot Schottky Diodes for RECTENNA (Rectifying Antenna)

In this paper we will present our latest research results of integrated quantum dot Schottky Diodes and integrated silicon antenna for RF applications. Both, the quantum dot Schottky diodes and the antenna are integrated on Si substrates forming a simple mm-wave detection system, the rectifying antenna (RECTENNA). Within this work a specific antenna design, 1-dimensional array (single line antenna), will be shown. First S-parameter measurement results up to 110GHz are very promising for system application in the 80 GHz automotive radar frequency band.

MBE growth of Ge quantum dot structures in oxide windows

The implementation of Quantum Dots (QDs) in devices allows novel electronic and opto-electronic functions. Strain driven Stranski-Krastanov growth mode enables the formation of nanometric islands (on wetting layer) whose density and geometry depend on growth conditions (temperature, rate) and surface structure (cleaning). The island positions are random. However, they can be influenced by surface patterning. In this work, the MBE growth of self-organized Ge QD structures in oxide windows is investigated. The studied Ge QD structures are composed by either a single Ge layer directly grown on a Si substrate, or double layer formed by a Ge QD layer on top of a Si buffer layer. Different surface preparation (dry etching with and without anisotropic wet etching) and cleaning (HF dip or RCA cleaning) schemes have been used. It is found that the cleaning and the Si buffer layer growth have strong influence on island nucleation. Preferred nucleation at the window edge and/or nucleation at the window center is observed under certain conditions. Interestingly, negligible influence (this is needed for most device works) is found only if Ge is grown directly on the RCA cleaned window.

Charge Carrier Traffic at Self-Assembled Ge Quantum Dots on Si

Due to their interesting size-dependent properties, semiconductor Quantum Dots (QDs) have many potential applications in nanoelectronics and optoelectronics. Ge QDs are particularly attractive because of the compatibility of Ge with Si technology and the ability to grow dislocation-free Ge QDs through the Stranski-Krastanov growth mode. Recently given examples include mm-wave circuit operation [1] with Ge QD Schottky diodes of 1.1 THz transit frequency or room temperature single electron memory [2] function of double (Si,Ge) dots. In this paper the voltage dependent occupation of states and their filling dynamics is investigated in two terminal device structures (Schottky barrier diode, p/n junction) by capacitance voltage (C-V) and deep level transient spectroscopy (DLTS) methods. Frequency scanned DLTS (FS-DLTS) was used, where the DLTS signal at a constant temperature is measured as a function of the repetition frequency of electrical pulses, f, with the emission voltage of the pulses, VR, as a parameter. Presenting DLTS spectra as a contour plot on a (f, VR)-plane, where contour lines with negative (positive) slope reflect signals related to thermal (tunnelling) transitions makes it possible to distinguish between these emission paths.

Ge quantum dot Schottky diode operated in a 89GHz Rectenna

Schottky diode structures with Ge quantum dots (QDs) have been grown by Molecular Beam Epitaxy (MBE). They have been employed to fabricate NiSi Schottky diodes with Ge dots buried below the metal-semiconductor junctions. These diodes have cut-off frequencies up to 1.1THz (calculated from S-parameter measurements up to 110GHz). Preliminary results demonstrating the implementation of Ge QD Schottky diode in a mm-wave power detection system (RECTENNA) are also presented.

Spatial Variation of Hole Eigen Energies in Ge/Si Quantum Wells

Ge quantum well (QW) structures were prepared through Si-capping of 3.3 ML of Ge by MBE on p +-(001) Si substrates at a growth temperature of 550°C. The spatial variation of hole eigen energies in the QW were revealed by DLTS. Depending on the position on the wafer surface, the hole emission may be imposed by a lateral quantum confinement effect. Results of a study by HRTEM methods demonstrate pronounced fluctuations of the QW thickness and variations of the strain field in the QW.