Back and front interface related generation-recombination noise inburied-channel SOI pMOSFETs

This paper reports on a detailed study of generation-recombination (GR) noise in buried-channel silicon-on-insulator (SOI) pMOSFETs, occurring in the linear operation mode. In particular, the plateau amplitude and the corner frequency (relaxation time τ) of the Lorentzian are investigated as a function of the front (V_Gf) and of the back gate bias (V_Gb). It is shown that different cases can be distinguished, depending of the conduction mode of the device, i.e. for surface or buried channel operation. For surface channel operation the GR noise parameters are strongly influenced by the back gate bias and only weakly dependent on V_Gf. The opposite is true when the front interface starts to deplete, thereby pushing the channel deeper into the Si film. As is shown, the relaxation time depends exponentially on either V_Gf or V_Gb. A similar exponential gate-bias dependence is found for the Lorentzian amplitude. Based on the observations, it is concluded that the GR noise originates from the front or the back interface, depending on the operation mode. The effective density of front and back interface traps can be derived from the GR noise amplitude     

Explaining the parameters of the electron valence-band tunneling related Lorentzian noise in fully depleted SOI MOSFETs

The behavior of the Lorentzian noise overshoot time constant /spl tau/ and plateau amplitude is investigated in fully depleted silicon-on-insulator MOSFETs with the back gate in accumulation. It is shown that /spl tau/ is identical for long-channel nand p-MOSFETs in the gate overdrive voltage range studied. For shorter lengths (L = 0.12 /spl mu/m), a slight reduction of /spl tau/ for the p-MOSFETs and an increase for the short n-MOSFETs has been found. The observations will be explained by considering both the injection of majority carriers in the floating body through electron valence-band tunneling and the dynamic resistance of the source-body and gate-body junction.     

High-frequency 1ƒ noise of photocurrent and residual conductivity in CdS

Peculiarities of the photocurrent noise and of the residual (“frozen”) conductivity are analyzed theoretically for the model of a CdS-type photoconductor. The significant element of this model is the existence of the collective recombination barrier. It is shown that in the cases where such a model is realized, the appearance of $\text{1}\text{?}$ portions in photocurrent noise spectra as well as in the noise spectra of the residual conductivity should be expected. Experiments are proposed and carried out which confirm the existence of the connection between the occurence of $\text{1}\text{?}$ portions in the noise spectra and the presence of the collective recombination barriers. Thus, the nature of the high-frequency $\text{1}\text{?}$ portions which have been often observed in photocurrent noise spectra of CdS is established. These have been erroneously ascribed to peculiarities of exchange between the c-band and the traps. The direct experimental proof of the dominating role of the recombination barriers in the residual conductivity phenomena is obtained.     

Electrical characterization of shallow cobalt-silicided junctions

The impact of the thickness of the cobalt-silicide layer on the electrical diode characteristics will be reported, with particular emphasis on the current-voltage (I-V characteristics, the surface and bulk carrier recombination lifetime and the low-frequency noise. It is shown that for thicker silicides the generation-recombination of holes in the top n⁺-layer is enhanced, giving rise to a higher diffusion current, an increase in the noise and a larger surface recombination velocity. It is believed that these parameters are closely linked, as the underlying physical phenomenon is the minority carrier recombination. In addition, it is shown by transmission electron microscopy that the silicide-silicon interface roughness is increased for larger cobalt thickness, which may explain some of the observations.     

The influence of BF2 and F implants on the 1/f noise inSiGe HBTs with a self-aligned link base

A study is made of 1/f noise in SiGe heterojunction bipolar transistors (HBTs) fabricated using selective growth (SEG) of the Si collector and nonselective growth (NSEG) of the SiGe base and Si emitter cap. The transistors incorporate a self-aligned link base formed by BF ₂ implantation into the field oxide below the p⁺ polysilicon extrinsic base. The influence of this BF₂ implant on the 1/f noise is compared with that of a F implant into the polysilicon emitter. Increased base current noise S_IB and base current are seen in transistors annealed at 975°C, compared with transistors annealed at 950 or 900°C. At a constant collector current, both the BF₂ and F implants reduce S_IB, whereas at a constant base current, only the BF₂ implant reduces S_IB. This result indicates that the BF₂ implant decreases the intensity of the base current noise source whereas the F implant decreases the base current. The proposed explanation for the increased 1/f noise is degradation of the surface oxide by viscous flow at 975°C under the influence of stress introduced during selective Si epitaxy. The influence of the BF₂ implant on the noise is explained by the relief of the stress and hence the prevention of viscous oxide flow     

RTS noise due to lateral isolation related defects in submicron nMOSFETs

The results of a systematic study of the random telegraph signal (RTS) fluctuations in submicron W-array n metal-oxide semiconductor field-effect transistors (nMOSFETs) are presented and analysed. These results include the dependency of the RTS amplitude and of the capture and emission time constants, measured both in the standard transistor and in the diode configuration, on the gate, drain and substrate voltage. For the latter configuration, the drain-substrate (or source-substrate) diode of the transistor is forward biased. Application of this technique for measuring RTS noise allows us to distinguish the drain (source) traps from the well-known channel traps. It is found that besides the classical channel-related RTSs, another type occurs which is associated with lateral isolation related (or edge-related) oxide defects, located near the drain or the source contact. As will be shown, the coulomb blockade significantly affects the capture and emission kinetics of these defects. The specific properties of such RTSs are studied in detail, as they may reveal useful information on their identification.     

Effect of illumination on noise and some other characteristics of p-n junctions in InSb

Spectra of low-frequency (f = 20 Hz-20 kHz) noise in InSb p-n junctions are investigated at different voltage biases and under different illumination intensities at T = 77°K.

It is found that fluctuations of ohmic leakage current are the main source of the current noise in the dark. Fluctuations of conduction of the space charge region (SCR) are observed only at sufficiently large forward biases. Under illumination fluctuations of the photocurrent make the essential contribution to the excess noises. It is shown that these fluctuations are generated in SCR and their peculiarities depend not only on the value of voltage bias but also on the level of illumination L. A variety of other characteristics of p-n junction are found to be conditioned by illumination level as well: with increasing L the photoelectric efficiency of the diode decreases, and an increase takes place in the equivalent differential conductivity of SCR as well as in the forward current measured at constant voltage biases on the p-n junction. Such changes may be explained either by a decrease of the carrier life-time in SCR or by an increase of the width of SCR.

Arguments are adduced supporting the supposition that excess fluctuations of conductivity of SCR arise only in some regions of SCR which are characterized by the specific mechanism of current conduction.     

Impact of cobalt silicidation on the low-frequency noise behaviorof shallow p-n junctions

This work describes the low-frequency noise of forward biased shallow p-n junctions fabricated in epitaxial silicon substrates. Particular emphasis is on the effect of silicidation on the low-frequency noise spectral density S_I. It is demonstrated that the observed 1/f noise is significantly larger in Co-silicided junctions compared with the nonsilicided ones. A detailed analysis of the current and geometry dependence of S_I leads to the conclusion that the 1/f noise is of the generation-recombination (GR) type, with the responsible GR centres homogeneously distributed over the device area. From the correlation with the forward current-voltage (I-V) characteristics, it is derived that GR fluctuations in the hole current through the n⁺ region cause the increased 1/f noise in the silicided devices