• Omar Abdulwahid

Student thesis: Phd


The work in this thesis was concerned with the analysis, modelling, design, testing and improvement of detectors using InP and GaAs-based technologies for electronic and optical receiver systems. For the electronic receivers, two types of Asymmetric Spacer Tunnel (ASPAT) diodes were studied and tested for potential microwave and mm-wave applications including novel X-band and K-band zero-bias tunnel diode frequency detectors. The core element of the detectors is a GaAs/AlAs ASPAT diode. DC and high-frequency S-parameter characterisation of diodes of mesa sizes of 1.6x1.6 square micrometre, 2.4x2.4 square micrometre‚3.7x3.7 square micrometre, 5.8x5.8 square micrometre and 10x10 square micrometre were carried out to fully extract their extrinsic and intrinsic components for optimum detector and 2nd subharmonic mixer circuits analysis and design. Coplanar waveguide matching circuit structures were designed and optimised to minimise the mismatch between the RF source and the diode impedance. The detectors were fabricated and experimentally measured in the frequency bands (4 to 18) GHz and (10 to 35) GHz at various input powers. The maximum measured sensitivity is 3650V/W and 1300V/W at 11GHz and 24GHz respectively for -27dBm incident RF power. The minimum calculated noise equivalent power is (~6pW/square root hertz) and (~20pW/square root hertz) for the X-band and K-band detectors, respectively. The 1.6x1.6 square micrometre ASPAT offered a maximum sensitivity of (1850V/W) at 250GHz. The ASPAT diodes were then used in a simulation work to test and examine their performance in mm-wave heterodyne circuits. At 77GHz RF signal, a moderate conversion loss of 10dB was achieved using the 3.7x3.7 square micrometre GaAs/AlAs, while a 16dB was obtained using the 3.75x3.75 square micrometre In0.53Ga0.47As/AlAs ASPAT diodes at 0dBm LO power. These detectors show excellent performances, comparable to reported X-band and K-band detectors based Schottky diodes but with the added advantage of stable operation over a wide temperature range. The results reported here validate the models developed which can be used to realise low cost, extremely low power, temperature-insensitive high-frequency tunnel diode detectors for a range of applications. The second part of the thesis dealt with telecommunication optoelectronic receivers. Validated SILVACO physical models were exploited to optimise the electrical and optical characteristics of 1.55 micrometre wavelength In0.53Ga0.47As/In0.52Al0.48As avalanche photodiodes (APD) and In0.53Ga0.47As PIN diodes. Optimised SILVACO models were created by selectively thinning down the absorption layers to further reduce the carrier transit time. Further optimisation was accomplished through scaling of the light window aperture and mesa area sizes to reduce the device capacitances. The optimised PIN diode provides a maximum optoelectric bandwidth of (35GHz) with a current responsivity of (0.4A/W) under -5V bias and (10 microwatts) incident optical power. At 1 microwatt incident optical power, the maximum optoelectric bandwidth and current responsivity of the optimised avalanche diode are (21GHz) and (1.4A/W) under -21.5V bias. The optimised avalanche and PIN photodetectors are capable of working at a data rate of up to 25Gb/s and 40Gb/s respectively.
Date of Award31 Dec 2019
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorMohamed Missous (Supervisor) & Massimiliano Migliorato (Supervisor)


  • Photodetector
  • RF detector
  • Small-signal equivalent circuit
  • ASPAT diode

Cite this