Semiconductor detectors have a wide range of uses for particle physics and synchrotron applications. This thesis concentrates on the simulation, fabrication and characterisation of a new type of detector known as the low gain avalanche detectors (LGAD). The detector’s characteristics are simulated via a full process simulation to obtain the required doping profiles which demonstrate the desired operational characteristics of high breakdown voltage (500V) and a gain of 10 at 200V reverse bias for low energy X-ray detection. The low gain avalanche detectors fabricated by Micron Semiconductor Ltd are presented. The doping profiles of the multiplication junctions were measured with Secondary ion mass spectrometry (SIMS) and reproduced by simulating the full fabrication process which enabled further development of the manufacturing process. LGADs are interesting for high energy physics experiments due to their good timing performance. The need for such a detector is explained and results for 250um thick LGADs with a gain of 5 manufactured at Micron Semiconductor show comparable results to the other vendors, of 120ps. For low energy X-ray detection it is essential to operate at low noise levels. The aim of the project was to develop LGAD detectors with a highly segmented front side which would be compatible with the Timepix3 chip, which has an array of 256x256 pixels with a pixel pitch of 55um. However, when LGAD pixels are made to these size requirements their gain uniformity and fill factor are extremely degraded. Specific development for small pixel LGAD's was undertaken through simulation and possible structures have been identified to minimize this small pixel effect.