3.   Limitations of past technologies and increased research into the structure of the atom resulted in the invention of transistors

• identify that some electrons in solids are shared between atoms and move freely

• perform an investigation to model the behaviour of semiconductors, including the creation of a hole or positive charge on the atom that has lost the electron and the movement of electrons and holes in opposite directions when an electric field is applied across the semiconductor
• gather, process and present secondary information to discuss how shortcomings in available communication technology lead to an increased knowledge of the properties of materials with particular reference to the invention of the transistor
• identify data sources, gather, process, analyse information and use available evidence to assess the impact of the invention of transistors on society with particular reference to their use in microchips and microprocessors
• identify data sources, gather, process and present information to summarise the effect of light on semiconductors in solar cells

• describe the difference between conductors, insulators and semiconductors in terms of band structures and relative electrical resistance

• identify absences of electrons in a nearly full band as holes, and recognise that both electrons and holes help to carry current

• compare qualitatively the relative number of free electrons that can drift from atom to atom in conductors, semiconductors and insulators

• identify that the use of germanium in early transistors is related to lack of ability to produce other materials of suitable purity

• describe how ‘doping’ a semiconductor can change its electrical properties

• identify differences in p and n-type semiconductors in terms of the relative number of negative charge carriers and positive holes

• describe differences between solid state and thermionic devices and discuss why solid state devices replaced thermionic devices