The type-II/InA1As avalanche photodiode and optimisation of avalanche photodiodes in receiver systems

Calculations based on a rigorous analytical model arc carried out to optimise the width of the avalanche region, w, in high-speed direct-detection avalanche photodiode- . based optical receivers. The model includes the effects of intersymbol interference (ISI), tunnelling current, avalanche noise, as well as dead space. The sensitivity of InP, InA1As and InAs avalanche photodiodes (APDs) were investigated. The interplay among the factors controlling the optimum sensitivity is confirmed. Results show that for a given transmission speed, as the device width decreases below the optimum value, increased tunnelling current outweighs avalanche noise reduction due to dead space, resulting in poorer receiver sensitivity. As the device width increases above its optimum value, the receiver sensitivity worsens as bandwidth decreases, causing TST to dominate avalanche noise and tunnelling current. For a 10 Gb/s system and a bit-error rate of 10.12, an optimum w of 0.191lm is predicted, yielding an optimum sensitivity of -28.1 dBm at an M of 13 for InP APDs. InAIAs APDs were found to provide an improvement of 0.5 dBm over InP at an M of 15 and w of 0.15Ilm. InAs APDs have been calculated to yield an optimum sensitivity between -29.6 and -30.2 dBm at an M of 76 and w of 4.2Ilm. A type-II InGaAs/GaAsSb superlattice p-i-n diode and separate absorption and multiplication (SAM) APD using TnAlAs as the multiplication region (both lattice- matched to InP) is reported. Optical and electrical characterisations of the devices are performed. The devices exhibited a cut-off wavelength of 2.511 m. Unity-gain responsivities of 0.53 A/W and 0.47 A/W have been obtained for the p-i-n diode and APD, respectively, when illuminated with 2.004f.lm wavelength light. Detectivity at this wavelength was calculated to be 7.1 x 10Y cmHzY'l/W for the p-i-n diode and 5.9x I O~ cmHz'f,/W for the APD. Excess noise measurements conducted on the APD show that the characteristics follow that of an In AlAs p-i-n diode with the same multiplication layer thickness, giving an effective k of 0.2. Significant multiplication factors, above 50 at 290K and above 200 at 200K, have also been achieved by the APD.EThOS - Electronic Theses Online ServiceGBUnited Kingdo