On wafer dark current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed at room temperature using a picoammeter (HP Model 4140B) and an LCR meter (HP Model 4275A), respectively. Temperature dependent I V measurements were performed using a Janis ST-500 cryogenic probe station. For I-V measurements, devices with diameters of 70, 120, 220 and 420 µm were characterised. Responsivity measurements at room temperature were performed by illuminating the top of mesa diodes of 420 µm diameter with 1520 nm wavelength light from a He-Ne laser. The resultant photocurrent was measured with a lock-in amplifier (Stanford Research Systems Model SR830) by a phase sensitive detection method. For electroluminescence (EL) measurements, mesa diodes of 420 µm diameter were wire bonded on 3 mm TO headers. A Keithley 2400 source-meter unit was used for continuous wave characterization and the EL spectra were collected using a 400 µm diameter core multimode optical fibre and a NIRQUEST-512-1.9 Ocean Optics spectrometer operating in 1100-1900 nm spectral range. 

Captions
Figure 1. (a) Reverse dark current density versus voltage for wafers A500 and A300. (b) Reverse dark current density versus voltage for all InGaAs wafers.

Figure 2. (a) Dark current density at a reverse bias of -1 V and (b) zero bias responsivity at 1520 nm, as a function of growth temperature. 

Figure 3. (a) Capacitance against reverse voltage characteristics of InGaAs p-i-n diodes. (b) Room temperature EL spectra of wafers A500, A300 and A250. 

Figure 4. (a) Arrhenius plot of dark current density at -1 V of A250 from 180 to 295 K. (b) Dark current data and modelling of A250. Inset shows the electric field versus applied voltage characteristics for the assumed doping profile.