Quantum Efficiency Of Photodiodes Research Articles

High quantum efficiency of UV-enhanced silicon photodiodes

High quantum efficiency UV-enhanced (P+nn+) silicon photodiodes have been developed using ion implantation, rapid thermal processing, and a thin silicon dioxide film as an antireflection/passivation layer. The unbiased devices have internal quantum efficiency in excess of 350% at a wavelength equal to 250 nm. The devices are stable, have very low dark current at a reverse bias voltage of 1 V and high responsivity. Analysis of the dopant concentration versus junction depth using a sheet resistance technique was done in this work. PACS Nos.: 85.60Gz, 85.60Bt, 85.60DW

A low voltage hybrid bulk/SOI CMOS active pixel image sensor

A hybrid bulk/silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) active pixel image sensor has been fabricated and studied. The active pixel comprised of reset and source follow transistors on the SOI thin film while the photodiode is fabricated on the SOI handling substrate after removing the buried oxide. The bulk photodiode can be optimized for efficiency with the use of lightly doped SOI substrate without compromising the circuit performance. On the other hand, the elimination of wells on the SOI thin-film allows the use of PMOSFET without increasing the pixel size. The addition of a PMOSFET in the active pixel structure can reduce the minimum operating voltage of the circuit beyond that of conventional designs. With the combination of the high quantum efficiency of bulk photodiode and the low power advantage of SOI technology, the hybrid technology is attractive for scaled low voltage imaging applications.

Quantum efficiency and dead time of single-photon counting photodiodes: a comparison between two measurement techniques

An experimental set-up based on correlated photons has been developed at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN) for the absolute measurement of the quantum efficiency and dead time of single-photon counting photodiodes. The overall accuracy is improved with respect to previously reported results, by using a thin and highly transmitting non-linear crystal. For comparison, a conventional set-up has been developed at 632.8 nm with a He-Ne laser, a trap detector and calibrated neutral-density filters. Measurements at different count levels have been performed with both techniques and results are compared for the quantum efficiency in the limit of zero count, η0, and for the dead-time measurement, tD. Contributions to the final uncertainty are analysed for both techniques. The results obtained are η0 = 0.3372 (standard uncertainty u(η0) = 0.0016) and tD = 33.8 ns (u(tD) = 2.0 ns) in the case of the two-photon technique and η'0 = 0.3376 (u(η'0) = 0.0036) and t'D = 31.7 ns (u(t'D) = 5.4 ns) in the case of the conventional technique.

Interpolation of the spectral responsivity of silicon photodetectors in the near ultraviolet

We improve the methods used to interpolate the responsivity of unbiased silicon photodetectors in the near-ultraviolet region. This improvement is achieved by the derivation of an interpolation function for the quantum yield of silicon and by consideration of this function in the interpolation of the internal quantum efficiency of photodiodes. The calculated quantum-yield and spectral-responsivity values are compared with measurement results obtained by the study of a silicon trap detector and with values reported by other research groups. The comparisons show agreement with a standard deviation of 0.4% between our measured and modeled values for both the quantum yield and the spectral responsivity within the wavelength region from 260 to 400 nm. The proposed methods thus extend the predictability of the spectral responsivity of silicon photodetectors to the wavelength region from 260 to 950 nm. Furthermore, an explanation is proposed for the change in the spectral responsivity of silicon photodiodes that is due to UV radiation. In our improved quantum efficiency model the spectral change can be accounted for completely by the adjustment of just one parameter, i.e., the collection efficiency near the SiO(2)/Si interface.

Improved ultraviolet quantum efficiency using a semitransparent recessed window AlGaN/GaN heterojunction p-i-n photodiode

We report on the improved quantum efficiency of GaN-based ultraviolet heterojunction photodiodes using a semitransparent recessed window device structure. At a reverse bias of −5 V the quantum efficiency was ∼57% at the band edge, and remained relatively flat down to ∼330 nm after which some absorption in the p-AlGaN layer became evident. The quantum efficiency only gradually declines after this point, remaining >20% at 280 nm. We attribute these results to avoidance of the optical dead space at the surface of GaN homojunction p-i-ns. The semitransparent p-AlGaN layer was comparatively resistive, causing an electric field crowding effect which resulted in a spatially nonuniform temporal behavior.

Field and temperature dependencies of the quantum efficiency of GaAs and GaP Schottky diodes

An experimental and theoretical study of GaAs and GaP Schottky photodiode quantum efficiency is reported. The quantum efficiency was investigated as a function of temperature in the 80-360 K interval and as a function of electric field in the space-charge region in the interval. The photocurrent is found to increase strongly with temperature, by a factor of three for GaP diodes and by a factor of six for GaAs diodes. We believe that this is evidence of a high concentration of imperfections in the space-charge region. These imperfections manifest themselves only in photoelectric properties. Such defects act as traps and capture both photoelectrons and photoholes. At low temperatures, most of the pairs recombine, but some fraction of them escape from the traps due to thermal excitation and give an electric current which rises with temperature. The time of the capture has to be of the order of the carrier drift time, . The electric field dependence of the quantum efficiency is also evidence of the high trap concentration. We believe that this is due to a field-induced shift of the carrier energy level in the trap. At high temperature, the photon energy and electric field dependencies of the photocurrent tend towards saturation.

A 1-Gb/s monolithically integrated silicon NMOS optical receiver

We report a monolithically integrated optical receiver consisting of a silicon NMOS transimpedance preamplifier paired with a lateral, interdigitated p-i-n photodiode. The photodiode's quantum efficiency was 82% at 850 nm, and it exhibited a dark current of 300 pA at -30 V. At the optimal operating point, the preamplifier achieved a bandwidth of 500 MHz, a transimpedance of 51.4 dB/spl middot//spl Omega/ and dissipated only 10.8 mW of power at a power supply voltage of 1.8 V. At a bit-error-rate of 10/sup -9/, the receiver exhibited sensitivities of -22.8, -15.0, and -9.3 dBm at bit rates of 622 Mb/s, 900 Mb/s, and 1 Gb/s, respectively.

Extension of a silicon-based detector spectral-responsivity scale into the ultraviolet

A detector spectral-responsivity scale based on the intrinsic properties of radiometric-quality photodiodes has previously been established over the wavelength range 400 nm to 900 nm. Work to extend this range into the ultraviolet below 400 nm is now being carried out. The new scale, which covers the 250 nm to 900 nm range, can be held in new four-element and five-element trap detectors. The precision of the scale in the ultraviolet is limited principally by the greater variations - across the detector surface and from one detector to another - of the internal quantum efficiency at these wavelengths. The actual internal quantum efficiency of S1337-11 Hamamatsu photodiodes obtained by our measurements is compared with previous experimental and calculated values for the quantum yield of silicon in this wavelength region.

Photodiode quantum efficiency optimization using spherical pits on active surfaces

A numerical model of a photodiode with etched spherical pits on an active surface has been developed. Several geometrical parameters (radius of curvature, depth and arrangement of spherical pits, sample thickness and area, and thickness of the anti-reflection layer) were varied and their influence on the quantum efficiency of the structure was considered. It has been shown that the photodiode quantum efficiency can be optimized by the proper choice of these parameters. From the technological point of view, it is very important that the optimized quantum efficiency can be achieved without a strict definition of the device geometry.

A discrete element model of laser beam induced current (LBIC) due to the lateral photovoltaic effect in open-circuit HgCdTe photodiodes

The non-destructive optical characterization technique of Laser-Beam-Induced-Current (LBIC) imaging has proven useful in qualitatively assessing electrically active defects and localized non-uniformities in HgCdTe materials and devices used for infrared photovoltaic arrays. To further the development of a quantitative working model for LBIC, this paper focuses on the application of the technique to photovoltaic structures that are represented by a discrete element equivalent circuit. For this particular case the LBIC signal arises due to the lateral photovoltaic effect in non-uniformly illuminated open-circuit photodiodes. The outcomes of the model predict all of the experimentally observed geometrical features of the LBIC image and signal. Furthermore, the model indicates that the LBIC signal has an extremely weak dependence on the p-n junction reverse saturation current, and shows a linear dependence with laser power. This latter feature map be useful for non-contact measurement of the quantum efficiency of individual photodiodes within a large two-dimensional focal plane array. The decay of the LBIC signal outside the physical boundary of the p-n junction is of the same form as the roll-off in the short circuit photoresponse and, therefore, can be used to extract the diffusion length of minority carriers. Experimental data is obtained from an arsenic implanted p-on-n junction fabricated on MBE grown Hg/sub 1-x/Cd/sub x/Te material with an x-value of 0.3. The p-on-n diode is shown to be uniform and of high quality with an R/sub 0/A product of 1/spl times/10/sup 8/ /spl Omega//spl middot/cm/sup 2/ at 77 K. The validity of the simple model developed in this paper, is confirmed by the excellent agreement with experimental results. Consequently, the LBIC technique is shown to be an appropriate diagnostic tool for non-contact quantitative analysis of semiconductor materials and devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Quantum efficiency and spectral response of compositionally graded HgCdTe P-n heterojunction photodiodes

Results are presented of a study of the quantum efficiency of HgCdTe heterojunction photodiodes. All heterojunctions considered in the study consist of a wide-band-gap P-type layer and a narrow-band-gap n-type layer, and are illuminated from the backside. The n-type layer is compositionally graded and therefore contains a built-in electric field. Due to the difference in band gaps photons are absorbed in the active n-type layer only and are collected by both drift and diffusion mechanisms. The one-dimensional continuity equation is first solved in the linearly graded n-type region under illumination conditions, and then the dependence of the quantum efficiency on the resulting built-in electric field is presented. Two different modes of illumination are compared: In the first mode, associated with n-on-P HgCdTe diodes, the light reaches the transparent P layer first; in the second mode, associated with P-on-n diodes, the light reaches the transparent P side after it passes through the opaque n-type layer. The superiority of the first mode is demonstrated: It consistently renders higher quantum efficiencies, and is also less sensitive to several properties of the diode such as the width of the absorbing layer and the quality of the backside interface.

Spectral response of a photodiode using 3C-SiC single crystalline film

Abstract 3C-SiC/Si heterojunction photodiodes and 3C-SiC homojunction photodiodes have been fabricated by atmospheric chemical vapor deposition. The maximum quantum efficiency of heterojunction photodiodes with a window layer of 10 μm thick is 80% at 550 nm. An increase in the thickness of the SiC layer reduces the responsivity in wavelength regions shorter and longer than 500–550 nm. 3C-SiC self supported films of 20 μm thick, epitaxially grown on Si, have been used as substrates for homojunction photodiodes. The responsivity of the homojunction photodiode with a window layer thickness of 0.5 μm is 72 mA/W at 250 nm with a quantum efficiency of 36%. When the thickness of the window layer is decreased, the peak responsivity increases and the peak wavelength shifts to a shorter wavelength. These spectral responsivities are discussed together with the results of calculations using a one-dimensional model.

Frequency Response and Quantum Efficiency of PIN Photodiode

Frequency Response and Quantum Efficiency of PIN Photodiode

Temperature dependence of CsI (T1) absolute scintillation yield

A cubic CsI(TI) crystal of 0.8 cm on a side was mounted on a 1 x 1 cm square photodiode to measure the absolute scintillation yield of CsI(TI) between - 100 and + 50°C. The room temperature yield was measured to be 64,800 + 3,200 photons/MeV. The maximum yield was observed to occur at about -35°C, approximately 6% above the room temperature yield. The yield was observed to decrease monotonically above and below this maximum. At - 100 and + 50°C the yield was measured to be about 64% and 95% of the room temperature yield, respectively. Over the range of - 55 to + 50°C the scintillation yield was observed to remain within +6% of the room temperature yield. The temperature dependence of scintillation decay time, scintillation emission spectrum, and wavelengthdependent photodiode quantum efficiency were considered.

Uniformity of Quantum Efficiency of Single and Trap-configured Silicon Photodiodes

We have carried out high resolution spatial measurements of the surface reflectance and responsivity of single and trap-configured silicon photodiodes at laser wavelengths between 325 nm and 780 nm. The results indicate that the spatial nonuniformity of quantum efficiency for a given photodiode varies with laser wavelength and internal structure. For radiometric quality diodes this nonuniformity of response leads to uncertainties in detector measurements which can be reduced to 0,03% or better.

A Physical Basis for the Extrapolation of Silicon Photodiode Quantum Efficiency into the Ultraviolet

The errors associated with modelling the quantum efficiency of high quality silicon photodiodes in the ultraviolet using the semiconductor device-modelling program PC1D are discussed. Uncertainty spectra have been calculated for these errors, which are mainly a result of the application of basic solid-state models and parameters in the extreme case of ultraviolet absorption. The more critical parameters have been identified and, where possible, corrections have been made to account for them. The overall uncertainty associated with quantum efficiency modelling is found to be well below 0,2% for detection of radiation from 400 nm to 300 nm, and below 1% for radiation down to 250 nm.

Calibration of silicon photodiodes by photoacoustics

We present a new approach to the calibration of silicon photodiodes that are used for light (radiometric) power measurements. We describe the photoacoustic method for the determination of internal quantum efficiency and absolute spectral response of silicon photodiodes in the photovoltaic short-circuit mode. Measurements were taken for the different structures of silicon photodiodes.

The quantum efficiency of HgCdTe photodiodes in relation to the direction of illumination and to their geometry

In this paper a theoretical study of the effect of the direction of the incident light on the quantum efficiency of homogeneous HgCdTe photodiodes suitable for sensing infrared radiation in the 8–12 μm atmospheric window is presented. The probability of an excess minority carrier to reach the junction is derived as a function of its distance from the edge of the depletion region. Accordingly, the quantum efficiency of photodiodes is presented for two geometries. In the first, the light is introduced directly to the area in which it is absorbed (opaque region), while in the second, the light passes through a transparent region before it reaches the opaque region. Finally, the performance of the two types of diodes is analyzed with the objective of finding the optimal width of the absorption area. The quantum efficiency depends strongly on the way in which the light is introduced. The structure in which the radiation is absorbed following its crossing the transparent region is associated with both higher quantum efficiency and homogeneity. In addition, for absorption region widths higher than a certain minimum the quantum efficiency in this case is insensitive to the width of the absorption region.

High quantum efficiency, long wavelength InP/InGaAs microcavity photodiode

There is an inherent tradeoff between the quantum efficiency and bandwidth of conventional pin photodiodes. In the case of devices based on III-V semiconductors, an absorption region thickness of approximately 2 μm is required to achieve quantum efficiencies greater than 80%, although this limits the transit-time-limited bandwidth to less than 15 GHz. It has recently been shown that a microcavity photodiode can circumvent this performance tradeoff and achieve both high quantum efficiency and large bandwidths. The fabrication of a microcavity pin photodiode with a high quantum efficiency near 1.55 μm is described. An external quantum efficiency of 82% at 1480 nm has been achieved with an InGaAs absorption layer only 2000 A thick embedded in a resonant cavity grown by metal organic vapour phase epitaxy (MOVPE).

Numerical modeling of silicon photodiodes for high-accuracy applications, Part I. simulation programs

The suitability of the semiconductor-device modeling program PC-1D for high-accuracy simulation of silicon photodiodes is discussed. A set of user interface programs optimized to support high-accuracy batch-mode operation of PC-1D for modeling the internal quantum efficiency of photodiodes is also described. The optimization includes correction for the dark current under reverse- and forward-bias conditions before calculating the quantum efficiency, and easy access to the highest numerical accuracy available from PC-1D, neither of which is conveniently available with PC-1D’s standard user interface.