A method utilising microwave plasma chemical vapour deposition (MPCVD) process of producing electronic device grade single crystal diamond comprising: (a) selecting a diamond seed or substrate having a pre-determined orientation; (b) cleaning and etching of non-diamond phases and other induced surface damages from the diamond seed or substrate, whereby this step is performed one or more times, and wherein this step comprises removing non-diamond phases from the substrate by cleaning it in a boiling acid bath having temperature greater than 300°C and subsequently plasma etching for 30 to 180 minutes, at an etching temperature from 700°C to 1200°C in a MPCVD chamber having an atmosphere with a pressure of 13.3 to 40 kPa (100 to 300 torr), and wherein the atmosphere therein comprises of 0.1% to 10% oxygen per unit of hydrogen; (c) growing a layer of extremely low crystal defect density diamond surface on the cleaned / etched diamond seed or substrate, whereby this step is performed one or more times as a pre-growth process for production of electronics device grade single crystal diamond by microwave plasma chemical vapour deposition (MPCVD) on the growth surface of the diamond seed, wherein the pre-growth process takes place at a temperature from 700°C to 1200°C in a MPCVD chamber, wherein the atmosphere comprises 1% to 15% CH 4 per unit of H 2 only, optionally with some additional mixture from 1% to 50% O 2 per unit of CH 4; and (d) growing electronics device grade single crystal diamond on top of the layer of the low crystal defect density diamond surface, wherein the growth rate of the electronics device grade single crystal diamond is 1 μm/hour to 15 μm/hour. (a) selecting a diamond seed or substrate having a pre-determined orientation; (b) cleaning and etching of non-diamond phases and other induced surface damages from the diamond seed or substrate, whereby this step is performed one or more times, and wherein this step comprises removing non-diamond phases from the substrate by cleaning it in a boiling acid bath having temperature greater than 300°C and subsequently plasma etching for 30 to 180 minutes, at an etching temperature from 700°C to 1200°C in a MPCVD chamber having an atmosphere with a pressure of 13.3 to 40 kPa (100 to 300 torr), and wherein the atmosphere therein comprises of 0.1% to 10% oxygen per unit of hydrogen; (c) growing a layer of extremely low crystal defect density diamond surface on the cleaned / etched diamond seed or substrate, whereby this step is performed one or more times as a pre-growth process for production of electronics device grade single crystal diamond by microwave plasma chemical vapour deposition (MPCVD) on the growth surface of the diamond seed, wherein the pre-growth process takes place at a temperature from 700°C to 1200°C in a MPCVD chamber, wherein the atmosphere comprises 1% to 15% CH 4 per unit of H 2 only, optionally with some additional mixture from 1% to 50% O 2 per unit of CH 4; and (d) growing electronics device grade single crystal diamond on top of the layer of the low crystal defect density diamond surface, wherein the growth rate of the electronics device grade single crystal diamond is 1 μm/hour to 15 μm/hour.