Papers by Author: Eugenijus Gaubas

Abstract: The characteristics of the band-to-band Auger recombination in Czochralski-grown high resistivity Si and Ge single crystals have been studied using a contactless technique to measure excess carrier decay transients based on infrared absorption by free carriers. The measurements are performed using laser light excitation with wavelengths ranging from 1.2 to 2.5 µm to reduce inhomogeneity effects in the extraction of the Auger recombination parameters. A linear approximation of the initial excess carrier decay lifetime yields an approximate value of the Auger recombination coefficient in Ge γ_A,Ge ≈ 2×10^-31 cm⁶/s, which is close to that in Si. These characteristics also indicate that the difference in Auger recombination coefficients for the ehh and eeh processes is small. A more detailed fitting procedure applied simultaneously on a series of experimental transients yields a more accurate value of (8±3)×10^-31 cm⁶/s for the Auger recombination coefficient in Ge.

Abstract: Results are presented of a comparative study of diodes processed on n-type Cz grown Si substrates without and with Ge doping concentration of about 10¹⁹ cm^-3 and 10²⁰ cm^-3. In order to investigate thermal donor formation, isothermal annealing at 450°C for 0.5 – 5 h was carried out. As processed diodes were also irradiated with 2 MeV electrons with fluences in the range between 10¹⁴ and 10¹⁷ e/cm² to investigate the Ge doping influence on irradiation induced defect formation. Diodes after thermal and radiation treatments have been investigated by combining different techniques.

Abstract: Results are presented of a comparative study of carrier lifetime in silicon and germanium. The impact of surface quality and passivation, of dopant type and concentration and of metallic impurities is studied using microwave probed free carrier absorption transient techniques.

Abstract: An overview is given of analytical techniques for the characterization of the electrical and transport parameters in thin (<1 µm) semiconductor layers. Some of these methods have been applied to the lifetime and diffusion length study in thin strain-relaxed buffer (SRB) layers of strained silicon (SSi) substrates, while a second group was dedicated to Silicon-on-Insulator (SOI) materials and devices. The employed techniques can be divided into two groups, whether a device structure (junction, MOS capacitor, MOSFET) is required or not. However, the MicroWave Absorption (MWA) technique can be used in both cases, making it a versatile tool to study both grown-in and processing-induced electrically active defects. The transport properties of SSi wafers are strongly determined by the density of threading and misfit dislocations, although the dependence of the recombination lifetime is weaker than expected from simple Shockley-Read-Hall (SRH) theory. This is related to the high injection regime typically employed, enabling the characterization of the 250-350 nm thick Si1-xGex layer only. At longer carrier decay times, multiple trapping events dominate that can be described by a stretched exponent approach, typical of disordered materials. For SOI substrates, transistor-based techniques will be demonstrated that enable to assess the generation or recombination lifetime in the thin silicon film (<100 nm). The lifetime can be severely degraded by irradiation or hot-carrier degradation. Finally, it will be shown that Generation-Recombination (GR) noise spectroscopy as a function of temperature allows identifying residual ion-implantation-damage related deep levels, which are otherwise hard to detect even by Deep Level Transient Spectroscopy (DLTS).

Abstract: The electrical activity of threading dislocations (TDs), occurring in a thin SiGe Strain Relaxed Buffer (SRB) layer has been investigated by a number of techniques and its impact on the reverse current of p-n junction diodes has been evaluated. It is shown that besides the density of TD, there are at least two other parameters playing an important role. The distance with respect to the metallurgical junction of the 5 nm C-rich layer, used for the strain relaxation and the dopant type in the well region also affect the leakage current. This complex behaviour is further reflected in the Emission Microscopy (EMMI) images, showing different breakdown sites for p+/n or n+/p junctions. Results will be presented whereby one of these parameters is varied, while the others are kept constant, in order to arrive at some idea of the relative importance of the different factors.