Excess Noise Characteristics Research Articles

Performance of a bridge-type TES microcalorimeter, excess noise characteristics and dependence of sensitivity on current

Fully utilizing the benefit of strong electrothermal feedback, we achieved the energy resolution of 6.6 eV (FWHM) at 5.9 keV and a fast response time of 74 μs with our bridge-type Ti/Au transition-edge sensor (TES) microcalorimeter. The energy resolution of this device was limited by a noise that was larger than the intrinsic noise and the readout noise. This noise only appeared when the current through the TES was large (≳10 μA) , and its level, defined as a fluctuation amplitude of the current through the TES, was in proportion to the inverse of the TES resistance. We also found that the TES sensitivity depended on the current through the TES, normalized with the critical current of the TES. When the current exceeded about 1% of the critical current, the TES sensitivity was significantly degraded. The critical current clearly correlated with the TES sensitivity, and hence the signal-to-noise ratio at the optimal operating point, among devices with different TES size and thickness. Thus, the critical current is one of the key parameters to determine the performance of the TES microcalorimeter.

Nonlocal effects in thin 4H-SiC UV avalanche photodiodes

The avalanche multiplication and excess noise characteristics of 4H-SiC avalanche photodiodes with i-region widths of 0.105 and 0.285 /spl mu/m have been investigated using 230-365-nm light, while the responsivities of the photodiodes at unity gain were examined for wavelengths up to 375 nm. Peak unity gain responsivities of more than 130 mA/W at 265 nm, equivalent to quantum efficiencies of more than 60%, were obtained for both structures. The measured avalanche characteristics show that /spl beta/>/spl alpha/ and that the /spl beta///spl alpha/ ratio remains large even in thin 4H-SiC avalanche regions. Very low excess noise, corresponding to k/sub eff/<0.15 in the local noise model, where k/sub eff/=/spl alpha///spl beta/(/spl beta///spl alpha/) for hole (electron) injection, was measured with 365-nm light in both structures. Modeling the experimental results using a simple quantum efficiency model and a nonlocal description yields effective ionization threshold energies of 12 and 8 eV for electrons and holes, respectively, and suggests that the dead space in 4H-SiC is soft. Although dead space is important, pure hole injection is still required to ensure low excess noise in thin 4H-SiC APDs owing to /spl beta///spl alpha/ ratios that remain large, even at very high fields.

Excess noise and other important characteristics of low light level imaging using charge multiplying CCDs

This paper describes recent progress in technology of low light level image sensing using CCD sensors that multiply charge by impact ionization before its conversion into a voltage. The paper presents a brief description of the concept, the outline of a typical sensor design with some important details related to prevention of serial register blooming and achieving high dynamic range (DR), and then focuses primarily on the measurement and analysis of noise components that are important in these devices. The paper describes the theory of excess noise, shows the computation of the output signal probability distribution function (PDF), and the derivation of formula for the excess noise factor (ENF). Finally, it is concluded that under suitable conditions it is possible to achieve a single photon (electron) detection (SPD) performance.

Multiplication and excess noise characteristics of thin 4H-SiC UV avalanche photodiodes

The avalanche multiplication and excess noise characteristics of thin 4H-SiC avalanche photodiodes with an i-region width of 0.1 /spl mu/m have been investigated. The diodes are found to exhibit multiplication characteristics which change significantly when the wavelength of the illuminating light changes from 230 to 365 nm. These multiplication characteristics show unambiguously that /spl beta/>/spl alpha/ in 4H-SiC and that the /spl beta///spl alpha/ ratio remains large even in thin 4H-SiC diodes. Low excess noise, corresponding to k=0.1 in the local model where k=/spl alpha///spl beta/ for hole injection, was measured using 325-nm light. The results indicate that 4H-SiC is a suitable material for realizing low-noise UV avalanche photodiodes requiring good visible-blind performance.

Al0.8Ga0.2As: A very low excess noise multiplication medium for avalanche photodiodes

The maximum useful gain of an avalanche photodiode is limited by the excess noise introduced by the stochastic nature of avalanche multiplication. Low avalanche excess noise can only be achieved in bulk materials with disparate electron and hole ionisation coefficients (α and β). The avalanche excess noise of bulk AlxGa1−xAs (x≤0.6) is relatively large as a result of α/β ratios that are close to unity. On the other hand, there is no information on the excess noise characteristics of bulk AlxGa1−xAs with x>0.6. A series of bulk Al0.8Ga0.2As p-i-n and n-i-p diodes were grown and characterised to investigate avalanche behaviour. Measurements indicate that bulk Al0.8Ga0.2As exhibit very low avalanche excess noise as a result of the significantly larger α/β ratio. This silicon-like characteristic is in stark contrast to that of almost all other III–V semiconductors, including InP. The results suggest that low-noise GaAs-based APDs can be realised using Al0.8Ga0.2As as the multiplication medium.

Scaling law of resistance fluctuations in stationary random resistor networks

In a random resistor network we consider the simultaneous evolution of two competing random processes consisting in breaking and recovering the elementary resistors with probabilities W(D) and W(R). The condition W(R)>W(D)/(1+W(D)) leads to a stationary state, while in the opposite case, the broken resistor fraction reaches the percolation threshold p(c). We study the resistance noise of this system under stationary conditions by Monte Carlo simulations. The variance of resistance fluctuations <deltaR2> is found to follow a scaling law |p-p(c)|(-kappa(0)) with kappa(0) = 5.5. The proposed model relates quantitatively the defectiveness of a disordered media with its electrical and excess-noise characteristics.

Excess Noise Characteristics of Hydrogenated Amorphous Silicon Avalanche Photodiode Films Using Functionally Graded Structure

An a-Si:H/a-SiC:H staircase photodiode with linearly graded gap multiplication regions is a useful device for photoconversion films. Photocurrent multiplication due to impact ionization was observed in the hydrogenated amorphous silicon (a-Si:H)/hydrogenated amorphous silicon carbide (a-SiC:H) staircase photodiode. In the staircase photodiode with one band offset, the photocurrent was multiplied twice and was saturated. In the staircase photodiode with three band offsets, a saturated multiplication gain of about 6 was obtained. The noise characteristics of the a-Si:H/a-SiC:H staircase photodiode films with one and three linear graded-gap regions were studied. The measured shot noise characteristics of the photodiode film, which was operated in a photocurrent multiplication region, corresponded to the ideal value, which was calculated as free excess noise. It was determined that the shot noise of a-Si:H/a-SiC:H staircase avalanche photodiode film was much less than that for the conventional crystal silicon avalanche photodiode in the photocurrent multiplication region. These results indicate that staircase photodiode films are promising devices for highly sensitive imaging sensors.

High-speed, high-reliability planar-structure superlattice avalanche photodiodes for 10-Gb/s optical receivers

This paper reports the planar-structure InAl-GaAs-InAlAs superlattice avalanche photodiodes (SL-APDs) with a Ti-implanted guard-ring, which were developed for a compact and high-sensitivity 10-Gb/s optical receiver application. The design and fabrication of the novel concept planar-structure including the Ti-implanted guard-ring are described. The characteristics of the planar APDs are 0.36 /spl mu/A dark current at a multiplication factor of 10, 67% quantum efficiency, 110-GHz gain-bandwidth (GB) product, 15-GHz top-bandwidth, and - 27.2-dBm sensitivity at 10 Gb/s. The reliability was preliminary tested and the lifetime of longer than 10/sup 7/ h at 50/spl deg/C was estimated. The dark current characteristics including its temperature dependence and the excess noise characteristics are also analyzed. All the obtained characteristics exhibit the practical availability of the planar SL-APDs in the 10-Gb/s trunk line optical receiver uses.

Excess noise characteristics of amorphous silicon staircase photodiode films

An a-Si:H (hydrogenated amorphous silicon)/a-SiC:H (hydrogenated amorphous silicon carbide) staircase photodiode with linear graded-gap multiplication regions is useful for photoconversion. Noise characteristics of the a-Si:H/a-SiC:H staircase photodiode films with one and three linear graded-gap region were studied. The measured shot-noise characteristics of the photodiode film, which was operated in a photocurrent multiplication region, corresponded to the ideal value which was calculated as free-excess noise. It was found that in the graded-gap region, the a-Si:H/a-SiC:H staircase photodiode film does not generate extra noise during the photocurrent multiplication. These results indicate that the staircase photodiode films are a promising device for the high-sensitive imaging sensor.

Gain properties of doped GaAs/AlGaAs multiple quantum well avalanche photodiode structures

A comprehensive characterization has been made of the static and dynamical response of conventional and multiple quantum well (MQW) avalanche photodiodes (APDs). Comparison of the gain characteristics at low voltages between the MQW and conventional APDs show a direct experimental confirmation of a structure-induced carrier multiplication due to interband impact ionization. Similar studies of the bias dependence of the excess noise characteristics show that the low-voltage gain is primarily due to electron ionization in the MQW-APDs, and to both electron and hole ionization in the conventional APDs. For the doped MQW APDs, the average gain per stage was calculated by comparing gain data with carrier profile measurements, and was found to vary from 1.03 at low bias to 1.09 near avalanche breakdown.

Temperature Dependence of Ionization Coefficients for InP and 1.3 µm InGaAsP Avalanche Photodiodes

Investigations were made on the temperature dependence of excess noise characteristics for InP and 1.3 µm InGaAsP APDs for the case where electrons are injected into the high field region. The effective ratio of the ionization coefficients Keff(β/α) was found to decrease with decreasing temperature for both APDs. Theoretical investigations on hot carriers are combined with McIntyre's theory for the excess noise characteristics to explain the experimental results. The dominant scattering process for hot electrons is the intervalley scattering; this leads to the fact that the temperature dependence of the mean free path is greater in the case of electrons than holes. The theoretical analysis provides the best fit to the experimental results. On the basis of the theoretical results, the compositonal dependence of the mean free path for hot electrons is discussed.

Ionization coefficients of Ga0.72Al0.28Sb avalanche photodetectors

The performance of an optical receiver depends heavily on the excess multiplication noise characteristics of the avalanche photodetector. The excess multiplication noise factor of an avalanche photodiode depends on the ratio of the electron and hole ionization coefficients. The ionization coefficients of 1.06-μm photodiodes fabricated from Ga0.72Al0.28Sb have been measured. The results show a hole-to-electron ionization-coefficient ratio of 2, which implies an excess gain noise factor F of 5.9 when the diode is operated at a gain of 10.

Noise characteristics of ion-implanted MOS transistors

Low-frequency excess noise characteristics of ion-implanted MOS transistors annealed above 1000 °C were investigated. Noise characteristics strongly depended on implant species, implant condition, and measurement conditions. In the case of implantation into opposite-type conductivity substrates, such as 11B+-implanted p-channel or 31P+-implanted n-channel transistors, the equivalent input noise voltages measured at lower drain currents exhibited generation-recombination (G-R) noise caused by residual damage in the substrate. This noise component increased with increasing acceleration energy or implant dose. The G-R noise decreased with increasing drain current. At higher drain currents the G-R noise disappeared and the noise voltages of the implanted samples were somewhat smaller than that of the unimplanted samples. On the contrary, in the case of implantation into the same-type conductivity substrate, such as 31P+-implanted p-channel or 11B+-implanted n-channel transistors, no G-R noise component was observed and noise voltages increased with increasing dose. The difference was also observed in the surface recombination velocity measurements. These results could be attributed to the difference in the position of the carrier path due to the change of surface band bending. The G-R noise could not be removed by heat treatment up to 1200 °C. It was confirmed that there were no dose rate dependences within the range 0.1–10 nA/cm2.