Avalanche multiplication in AlxGa1-xAs (x=0to0.60)

Electron and hole multiplication characteristics, Me and Mh, have been measured in AlxGa1-xAs (x=0-0.60) homojunction p+-i-n+ diodes with i-region thicknesses, w, from 1 μm to 0.025 μm and analyzed using a Monte Carlo model (MC). The effect of the composition on both the macroscopic multiplication characteristics and microscopic behavior is therefore shown for the first time. Increasing the alloy fraction causes the multiplication curves to be shifted to higher voltages such that the multiplication curves at any given thickness are practically parallel for different x. The Me/Mh ratio also decreases as x increases, varying from ~2 to ~1 as x increases from 0 to 0.60 in a w=1 μm p+-i-n+. The Monte-Carlo model is also used to extract ionization coefficients and dead-space distances from the measured results which cover electric field ranges from ~250 kV/cm-1200 kV/cm in each composition. These parameters can be used to calculate the nonlocal multiplication process by solving recurrence equations. Limitations to the applicability of field-dependent ionization coefficients are shown to arise however when the electric-field profile becomes highly nonunifor

Effect of impact ionization in the InGaAs absorber on excess noise of avalanche photodiodes

The effects of impact ionization in the InGaAs absorption layer on the multiplication, excess noise and breakdown voltage are modeled for avalanche photodiodes (APDs), both with InP and with InAlAs multiplication regions. The calculations allow for dead space effects and for the low field electron ionization observed in InGaAs. The results confirm that impact ionization in the InGaAs absorption layer increases the excess noise in InP APDs and that the effect imposes tight constraints on the doping of the charge control layer if avalanche noise is to be minimized. However, the excess noise of InAlAs APDs is predicted to be reduced by impact ionization in the InGaAs layer. Furthermore the breakdown voltage of InAlAs APDs is less sensitive to ionization in the InGaAs layer and these results increase tolerance to doping variations in the field control layer

Field dependence of impact ionization coefficients in In0.53Ga0.47As

Electron and hole ionization coefficients in In/sub 0.53/Ga/sub 0.47/As are deduced from mixed carrier avalanche photomultiplication measurements on a series of p-i-n diode layers, eliminating other effects that can lead to an increase in photocurrent with reverse bias. Low field ionization is observed for electrons but not for holes, resulting in a larger ratio of ionization coefficients, even at moderately high electric fields than previously reported. The measured ionization coefficients are marginally lower than those of GaAs for fields above 250 kVcm/sup -1/, supporting reports of slightly higher avalanche breakdown voltages in In/sub 0.53/Ga/sub 0.47/As than in GaAs p-i-n diodes

The effects of nonlocal impact ionization on the speed of avalanche photodiodes

The nonlocal enhancement in the velocities of charge carriers to ionization is shown to outweigh the opposing effects of dead space, increasing the avalanche speed of short avalanche photodiodes (APDs) over the predictions of a conventional local model which ignores both of these effects. The trends in the measured gain-bandwidth product of two short InAlAs APDs reported in the literature support this result. Relatively large speed benefits are predicted to result from further small reductions in the lengths of short multiplication regions

Avalanche noise characteristics of single Al/sub x/Ga/sub 1-x/As(0.3

Avalanche multiplication and excess noise have been measured on a series of Al/sub x/Ga/sub 1-x/As-GaAs and GaAs-Al/sub x/Ga/sub 1-x/As (x=0.3,0.45, and 0.6) single heterojunction p/sup +/-i-n/sup +/ diodes. In some devices excess noise is lower than in equivalent homojunction devices with avalanche regions composed of either of the constituent materials, the heterojunction with x=0.3 showing the greatest improvement. Excess noise deteriorates with higher values of x because of the associated increase in hole ionization in the Al/sub x/Ga/sub 1-x/As layer. It also depends critically upon the carrier injection conditions and Monte Carlo simulations show that this dependence results from the variation in the degree of noisy feedback processes on the position of the injected carriers

Avalanche multiplication and breakdown in AlxGa1-xAs (x < 0-9)

Measurements carried out on thick Al/sub x/Ga/sub 1-x/As (x 0.63

Low multiplication noise thin Al0.6Ga0.4As avalanche photodiodes

Avalanche multiplication and excess noise were measured on a series of Al0.6Ga0.4As p+in+ and n+ip+ diodes, with avalanche region thickness, w ranging from 0.026 μm to 0.85 μm. The results show that the ionization coefficient for electrons is slightly higher than for holes in thick, bulk material. At fixed multiplication values the excess noise factor was found to decrease with decreasing w, irrespective of injected carrier type. Owing to the wide Al0.6Ga0.4As bandgap extremely thin devices can sustain very high electric fields, giving rise to very low excess noise factors, of around F~3.3 at a multiplication factor of M~15.5 in the structure with w=0.026 μm. This is the lowest reported excess noise at this value of multiplication for devices grown on GaAs substrates. Recursion equation modeling, using both a hard threshold dead space model and one which incorporates the detailed history of the ionizing carriers, is used to model the nonlocal nature of impact ionization giving rise to the reduction in excess noise with decreasing w. Although the hard threshold dead space model could reproduce qualitatively the experimental results, better agreement was obtained from the history-dependent mode

Excess noise characteristics of Al0.8Ga0.2As avalanche photodiodes

The avalanche noise characteristics of Al0.8Ga0.2 As have been measured in a range of p-i-n and n-i-p diodes with i-region widths ω varying from 1.02 to 0.02 μm. While thick bulk diodes exhibit low excess noise from electron initiated multiplication, owing to the large α/β ratio (1/k), the excess noise of diodes with ω < 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 Al0.8Ga0.2As multiplication layers can give very low excess noise and that electrons must initiate multiplication to minimize excess noise, even in thin structure

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 µm 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 β > α in 4H-SiC and that the β/α ratio remains large even in thin 4H-SiC diodes. Low excess noise, corresponding to k=0.1 in the local model where k=α/β 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