N. Sustersic

Sensitivity of a vanadium oxide uncooled microbolometer array for terahertz imaging

The broadband imaging capabilities of a vanadium oxide microbolometer camera were investigated in the far-infrared for applications in real-time terahertz imaging and analysis. To accomplish this, we used an optical configuration consisting of a broadband terahertz source, terahertz filtering optics, and a modified commercial broadband microbolometer camera. A blackbody radiator was employed as the broadband terahertz source to illuminate the microbolometer array with all components in a nitrogen purged enclosure. Data was taken using several different levels of radiant flux intensity. Optical filtering were necessary to isolate incident radiation frequencies into a band from 1.5 to 7.5 THz. Fourier transform infrared spectroscopy was used to characterize the transmission properties of each optical component. The noise equivalent differential temperature (NEDT) and the noise equivalent power (NEP) were recorded over a range of blackbody intensities. We discuss the relative utility of these two figures of merit for terahertz imaging. For example, at a blackbody temperature of 925°C the NEDT was recorded below 800 mK, and the NEP was calculated to be 136 pW/√Hz. This study provides a complete analysis of a microbolometer as the detector component of a terahertz imaging system in a broadband imaging configuration.

Effects of boron and phosphorus doping on the photoluminescence of self-assembled germanium quantum dots

The doping of Ge quantum dots grown on Si (100) was investigated using atomic force microscopy and photoluminescence spectroscopy. The dots produced photoluminescence in the energy range from 0.75 to 0.95 eV. Compared to the undoped dots, the boron and phosphorus doped dots demonstrated a shift in peak emission toward lower energy by 60–80 meV, which is attributed to the decrease in density of the smaller sized dots. Increased photoluminescence intensity with temperature indicated higher activation energy with doping, suggesting a higher probability of radiative transitions at elevated temperatures, potentially important for various applications.

Structural and optoelectronic properties of germanium-rich islands grown on silicon using molecular beam epitaxy

We report on the structural and optoelectronic properties of self-assembled germanium-rich islands grown on silicon using molecular beam epitaxy. Raman, photocurrent, photoluminescence, and transient optical spectroscopy measurements suggest significant built-in strains and a well-defined interface with little intermixing between the islands and the silicon. The shape of these islands depends on the growth conditions and includes pyramid, dome, barn-shaped, and superdome islands. Most importantly, we demonstrate that these germanium-rich islands provide efficient light emission at telecommunication wavelengths on a complementary metal-oxide semiconductor-compatible platform.

Increasing the operating temperature of boron doped silicon terahertz electroluminescence devices

High power electroluminescence near 8THz was observed from boron doped silicon devices operating at heat sink temperatures up to 118K. This represents the highest emission temperature yet observed for silicon dopant-based terahertz devices, and is a significant increase from previous reports. This letter compares the temperature dependence of the emission mechanism to the dopant occupation function and describes an empirical model that fits the variation of output power with temperature, and that can guide the design of future terahertz devices.

Deep-level spectroscopy studies of confinement levels in SiGe quantum wells

The recharging of quantum confinement levels in SiGe quantum wells (QWs) was studied by charge deep-level transient spectroscopy (Q-DLTS) for Si/SiGe/Si structures with different Ge contents in the SiGe layer. The set of levels were observed as the different slopes in the Arrhenius plots for the same Q-DLTS peak in different temperature ranges. These activation energies were compared to the energies of quantum confinement levels in the QW calculated in frames of six-band model taking into account spin-orbit interaction and attributed to a thermally activated tunneling of holes from the SiGe QW.

Structural and light-emission properties of bulk Germanium islands grown on Silicon using Molecular Beam Epitaxy

We report on the optoelectronic properties of bulk Germanium islands formed on Silicon by Molecular Beam Epitaxy. More specifically, we will discuss the role of strains and doping in favoring efficient light-emission at telecommunication wavelengths.

Confinement Levels in Passivated SiGe/Si Quantum Well Structures

The set of quantum confinement levels in SiGe quantum wells (QW) was observed in the temperature range from 80 to 300 K by means of charge deep-level transient spectroscopy (Q-DLTS) and transport measurements. These observations proved possible due to a passivation of structure surface with organic monolayer deposition. Si/SiGe/Si structures with different Ge contents in SiGe layer were studied. The confined levels in passivated structures became apparent through DLTS measurements as various activation energies in temperature dependence of the rate of carrier emission from QW. It was found that the recharging of SiGe QWs and carrier emission accomplish due to thermo-stimulated tunneling. The steps in the current-voltage characteristics originated from direct tunneling via the confined states were found to determine the current flow at high fields.

Optoelectronic Properties of Germanium Islands Formed on Silicon Using Stranski-Krastanov Growth by MBE

We report on the optoelectronic properties of bulk Germanium islands formed on Silicon by Molecular Beam Epitaxy. More specifically, we will discuss the role of strains and doping in favoring efficient light-emission at telecommunication wavelengths.