Multiplication Layer Research Articles

Geiger mode operation of an In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode

Low-temperature photon counting with gated mode quenching is demonstrated with separate absorption, charge, and multiplication avalanche photodiodes that have an In/sub 0.52/Al/sub 0.48/As multiplication layer. A minimum of ten dark counts per second and single-photon detection efficiency of 16% were achieved at 130 K.

Optimal excess noise reduction in thin heterojunction Al/sub 0.6/Ga/sub 0.4/As-GaAs avalanche photodiodes

It has been recently found that the initial-energy effect, which is associated with the finite initial energy of carriers entering the multiplication region of an avalanche photodiode (APD), can be tailored to reduce the excess noise well beyond the previously known limits for thin APDs. However, the control of the initial energy of injected carriers can be difficult in practice for an APD with a single multiplication layer. In this paper, the dead-space multiplication recurrence theory is used to show that the low noise characteristics associated with the initial-energy effect can be achieved by utilizing a two-layer multiplication region. As an example, a high bandgap Al/sub 0.6/Ga/sub 0.4/As material, termed the energy-buildup layer, is used to elevate the energy of injected carriers without incurring significant multiplication events, while a second GaAs layer with a lower bandgap energy is used as the primary carrier multiplication layer. Computations show that devices can be optimally designed through judicious choice of the charge-layer width to produce excess noise factor levels that are comparable to those corresponding to homojunction APDs benefiting from a maximal initial-energy effect. A structure is presented to achieve precisely that.

InGaAs/InAlAs avalanche photodiode with undepleted absorber

We report an avalanche photodiode with an undepleted p-type InGaAs absorption region and a thin InAlAs multiplication layer. The motivation for utilizing an undepleted absorption layer, which is similar to that in the unitraveling carrier photodiode, is to reduce the dark current. A dark current below 1 nA at a gain of 10 and a gain–bandwidth product of 160 GHz are demonstrated.

Modeling and optimization of resonant cavity enhanced-separated absorption graded charge multiplication-avalanche photodetector (RCE-SAGCM-APD)

In this paper, a physical model of the Resonant Cavity Enhanced-Separated Absorption Graded Charge Multiplication-Avalanche Photodetector (RCE-SAGCM-APD) is presented. First, a SPICE model for RCE-SAGCM-APD is presented showing the dependence of the transfer function of this model on the dimensions, the material parameters and the multiplication gain of the photodetector. The results obtained from this SPICE model are compared with published experimental results and good agreement is obtained. The present SPICE model can also be applied to non RCE-APD and to different versions of avalanche photodetectors by modifying its transfer function. The gain-bandwidth characteristic of RCE-APD is studied for different areas and different values of the thicknesses of both the absorption and the multiplication layers. The gain-bandwidth characteristic of RCE-SAGCM-APD is studied for the case of an inductor added in series to the load resistance and better performance is achieved in comparison to the case with no inductance. The photodetector with and without the inductor is optimized to get the best values of thicknesses of both absorption and multiplication layers and also the optimal values of the series inductance. These optimizations are done for different areas of the photodetector, different multiplication gains and also for different load resistances.

Breakdown probabilities for thin heterostructure avalanche photodiodes

The recurrence theory for the breakdown probability in avalanche photodiodes (APDs) is generalized to heterostructure APDs that may have multiple multiplication layers. The generalization addresses layer-boundary effects such as the initial energy of injected carriers as well as the layer-dependent profile of the dead space in the multiplication region. Reducing the width of the multiplication layer serves to both downshift and sharpen the breakdown probability curve as a function of the applied reverse-bias voltage. In structures where the injected carriers have an initial energy that is comparable to the ionization threshold energy, the transition from linear mode to Geiger-mode is more abrupt than in structures in which such initial energy is negligible. The theory is applied to two recently fabricated Al/sub 0.6/Ga/sub 0.4/As-GaAs heterostructure APDs and to other homostructure thin GaAs APDs and the predictions of the breakdown-voltage thresholds are verified.

ORGANIC OPTICAL IMAGE PROCESSOR

The all-organic optical image processor was fabricated combining an organic electroluminescent (EL) layer with photocurrent multiplication layer. In this device, input light image from one side is once converted to a large photocurrent, which is fed to an EL layer emitting output light image from the other side with keeping the image pattern. The photocurrent multiplication in pigment-dispersed polymer films enabled us to fabricate a large area device suitable for image processors. The optical operation was realized by designing the output-input light intensity characteristics in this device. We demonstrated two types of optical image processing, “AND” and “OR”, for two input images.

Optimization of 10-Gb/s long-wavelength floating guard ring InGaAs-InP avalanche photodiodes

We demonstrate long-wavelength (/spl lambda/ = 1.3 and 1.5 μm) high-speed (10 Gb/s) InGaAs-InP separate absorption-grading-and-multiplication region avalanche photodiodes (SAGM-APDs) employing a double diffused floating guard ring (FGR) structure to eliminate edge breakdown. The simple /spl ges/ 60-GHz gain-bandwidth product double diffused FGR structure was optimized using theoretical and experimental studies. The APD excess noise factor was measured, and suggests that dead-length effects must be considered in designing high bandwidth devices with thin multiplication layers.

Gain-bandwidth characteristics of thin avalanche photodiodes

The frequency-response characteristics of avalanche photodiodes (APDs) with thin multiplication layers are investigated by means of a recurrence technique that incorporates the history dependence of ionization coefficients. In addition, to characterize the autocorrelation function of the impulse response, new recurrence equations are derived and solved using a parallel computer. The mean frequency response and the gain-bandwidth product are computed and a simple model for the dependence of the gain-bandwidth product on the multiplication-layer width is set forth for GaAs, InP, Al/sub 0.2/Ga/sub 0.8/As, and In/sub 0.52/Al/sub 0.48/As APDs. It is shown that the dead-space effect leads to a reduction (up to 30%) in the bandwidth from that predicted by the conventional multiplication theory. Notably, calculation of the power-spectral density of the photocurrent reveals that the presence of dead space also results in a reduction in the fluctuations in the frequency response. This result is the spectral generalization of the reduction in the excess noise factor in thin APDs and reveals an added advantage of using thin APDs in ultrafast receivers.

An analytical approach to study the effect of carrier velocities on the gain and breakdown voltage of avalanche photodiodes

A simplified model for calculating gain and breakdown voltage of avalanche photodiodes (APDs) having constant ionization coefficients in their multiplication layer is presented. Good agreement is seen between the calculated results and the experimental data for published InP-InGaAs separate absorption, grading, charge, and multiplication (SAGCM) APDs. The model denotes that the gain and the breakdown voltage have a dependence on the carrier velocity ratio that is not predicted by conventional models. Hence, by comparing the calculated and measured static characteristics of the APD, one can estimate the velocity of minority carriers in the multiplication region of the device.

Excess noise characteristics of Al/sub 0.8/Ga/sub 0.2/As avalanche photodiodes

The avalanche noise characteristics of Al/sub 0.8/Ga/sub 0.2/As have been measured in a range of p-i-n and n-i-p diodes with i-region widths /spl omega/ varying from 1.02 to 0.02 μm. While thick bulk diodes exhibit low excess noise from electron initiated multiplication, owing to the large /spl alpha///spl beta/ ratio (1/k), the excess noise of diodes with /spl omega/ < 0.31 μm were found to be greatly reduced by the effects of dead space. The thinnest diodes exhibit very low excess noise, corresponding to k = 0.08, up to a multiplication value of 90. In contrast to most III-V materials, it was found that both thick and thin Al/sub 0.8/Ga/sub 0.2/As multiplication layers can give very low excess noise and that electrons must initiate multiplication to minimize excess noise, even in thin structures.

Dark Current Reduction of Avalanche Photodiode Using Optimized InGaAsP/InAlAs Superlattice Structure

We studied reduction in dark current of avalanche photodiodes (APDs) using an optimized InGaAsP/InAlAs superlattice (SL) structure, which was fabricated by gas-source molecular beam epitaxy. For the sample which has the thickest barrier and the thinnest well, the dark current value of 0.4 µA at a multiplication factor of 10 was achieved. This is the lowest dark current for InGaAsP/InAlAs SL-APDs to our knowledge. This result shows that the band-to-band tunneling current, which affects dark current, was suppressed by increasing the effective band gap energy of the SL multiplication layer. Moreover, we discussed the mechanism of avalanche multiplication and confirmed the reason why sufficient avalanche multiplication occurred in optimized InGaAsP/InAlAs SL-APD even at low electric field. It was concluded that an optimized InGaAsP/InAlAs SL structure effectively enhances electron impact ionization and also improves dark current.

Growth, characterization and avalanche photodiode application of strain compensated InGaAsP/InAlAs superlattice

We applied InGaAsP/InAlAs strain compensated superlattice (SCSL) structure to the multiplication region of avalanche photodiode (APD) for the first time using gas-source molecular beam epitaxy. For the InGaAsP/InAlAs SCSL structure, material quality was evaluated by means of cross-sectional transmission electron microscope analysis and X-ray rocking curves. SCSL-APD device was fabricated and dark current property was also compared to normal InGaAsP/InAlAs superlattice avalanche photodiode (SL-APD). It was found that application of the SCSL structure to the multiplication layer in SL-APD improves the dark current property.

Impact ionisation coefficients of In0.53Ga0.47As

Ionisation coefficients were measured in a series of In0.53Ga0.47As p-i-n diodes with i-region thicknesses ranging from 1.82 µm to 4.60 µm. Pure electron injection and pure hole-like mixed injection measurements were made on the same p-i-n diodes to improve accuracy. Despite its narrow bandgap In0.53Ga0.47As is found to have a very similar breakdown voltage to that of GaAs. The measured ionisation coefficients are used to assess the feasibility of a homojunction In0.53Ga0.47As avalanche photodiode. Calculations suggest that such a device would need a very thick multiplication layer and high operating voltage to produce useful multiplication before tunnelling becomes significant.

Two-dimensional gain profiles of InP/InGaAs separate absorption, grading, charge, and multiplication avalanche photodiodes modeled by a simplified stochastic approach

The two-dimensional (2D) gain profiles of InP/InGaAs separate absorption, grading, charge, and multiplication (SAGCM) avalanche photodiodes (APDs) have been modeled by using a simplified stochastic approach. The influence of the curved diffusion edge on the electric field in the periphery has been considered and electric field equations have been derived from the cylindrical Poisson’s equation. The electric field in the multiplication layer is significantly reduced when a partial charge sheet is incorporated in the device’s periphery. The modeled 2D gain profile for such a device agrees with experiment and demonstrates an effective suppression of the premature edge breakdown. These results and the uniformity issue of the 2D gain profiles are further discussed. From our analyses, we find that controlling the diffusion process within the p+ InP top layer and patterning the charge sheet mesa structure are most likely to affect the uniformity and symmetry of the 2D gain profiles for the InP/InGaAs SAGCM APDs.

10 Gbit/s high sensitivity, low-voltage-operation avalanche photodiodes with thin InAlAs multiplication layer and waveguide structure

The development of waveguide avalanche photodiodes with a very thin 0.1 µm multiplication layer for use in high-speed, high-sensitivity, low-voltage-operation receivers is presented. A η = 76%, a GB product of 180 GHz, and a breakdown voltage Vb of 15 V were obtained. The 10 Gbit/s bit error rate measurement showed a sensitivity of –28.8 dBm (BER 10-9, PRBS 223–1), which is the highest sensitivity yet reported for APD receivers.

InAlAs avalanche photodiodes with very thin multiplication layer of 0.1 [micro sign]m for high-speed and low-voltage-operation optical receiver

We have developed a separated absorption and multiplication (SAM) avalanche photodiode (APD) with the thinnest reported InAlAs multiplication layer of 0.1 /spl mu/m and achieved 18.8 V operation. With high speed and a high GB product of 140 GHz. This makes it possible to realise a compact 10 Gbit/s APD receiver.

Modeling of two-dimensional gain profiles for InP-InGaAs avalanche photodiodes with a stochastic approach

The two-dimensional (2-D) gain profiles for separate absorption, grading, charge and multiplication (SAGCM) InP-InGaAs avalanche photodiodes (APD's) have been modeled with a stochastic approach. To consider the influence of the curved diffusion edge on the electric field within the periphery region, equations are derived from the cylindrical Poisson's equation. The electric field profiles are computed at various APD radii and the electric field in the multiplication layer is reduced significantly for APD's with a partial charge sheet in the periphery. It is demonstrated by the modeled 2-D gain profiles that the premature edge breakdown can be effectively suppressed for such devices. The modeled 2-D gain profiles for APD's with a partial charge sheet incorporated in the periphery are in good agreement with the experimental results. The results and the uniformity issue of the 2-D gain profiles are discussed. The effect of using curved diffusion interfaces instead of a steep mesa step is also explored; this suggests that the fabrication of a charge sheet mesa step may complicate the gain uniformity issue. From our analyses, we find that the uncertainty and the symmetry of both patterning the charge sheet mesa structure and controlling the diffusion interface between the p/sup +/ InP top layer and the n/sup -/ InP multiplication layer are most likely to affect the uniformity and the symmetry of the 2-D gain profiles for the SAGCM InP-InGaAs APD's.

In0.53Ga0.47As/In0.52Al0.48As separate absorption, charge, and multiplication layer long wavelength avalanche photodiode

The authors demonstrate the use of In/sub 0.52/Al/sub 0.48/As as the gain material in a separate absorption, charge, and multiplication layer avalanche photodiode (APD) with sensitivity to 0.9-1.7 /spl mu/m wavelength light. A hole to electron ionisation rate ratio of k=0.23 is observed, representing a significant improvement over the 1/k=0.4 characteristic of InP/In/sub 0.53/Ga/sub 0.47/As avalanche photodiodes. Primary dark currents of /spl sim/10 nA and gains approaching 100 for 100 /spl mu/m diameter mesa devices are observed. A 6 dB sensitivity advantage is measured for an APD receiver over an In/sub 0.53/Ga/sub 0.47/As p-i-n detector receiver at a wavelength of 1.55 /spl mu/m, a bit rate of 1.5 Gbit/s, and 10/sup -9/ bit error rate.

A new look at impact ionization-Part II: Gain and noise in short avalanche photodiodes

For Part I see R.J. McIntyre, ibid., vol.46, no.8, pp.1623-31 (1999). In Part I, a new theory for impact ionization that utilizes history-dependent ionization coefficients to account for the nonlocal nature of the ionization process has been described. In this paper, we will review this theory and extend it with the assumptions that are implicitly used in both the local-field theory in which the ionization coefficients are functions only of the local electric field and the new one. A systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses is also presented. It is demonstrated that there is a definite size effect for thin multiplication regions that is not well characterized by the local-field model. The new theory, on the other hand, provides very good fits to the measured gain and noise. The new ionization coefficient model has also been validated by Monte Carlo simulations.

Microlens-integrated large-area InAlGaAs-InAlAs superlattice APD's for eye-safety 1.5-μm wavelength optical measurement use

The advanced optical measurement system used in the eye-safety 1.5-/spl mu/m wavelength range requires high-sensitivity photodiodes with a large detecting area. For this purpose, we have developed large-area InAlGaAs-InAlAs superlattice avalanche photodiodes (SL-APD's) integrated with a monolithic microlens. By optimizing the superlattice multiplication layer as well as using a monolithically integrated microlens, a low multiplied dark current of 5 nA and a large detecting area of 200 /spl mu/m in diameter have been achieved for 100-/spl mu/m-mesa-diameter SL-APD's.