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The diffusion of dopants from the wafer surface into the semiconductor is an alternative to ion implantation for the introduction of charge carriers. The dopants can be introduced as a gas, a liquid, or from a previously deposited layer, which provides a constant concentration at the semiconductor interface. The depth of diffusion within the semiconductor is a function of temperature, so it must be carefully executed in order for further processing steps which require high temperatures, such as oxidation, do not damage the desired dopant concentration profile. The main advantages of diffusion over ion implantation is that diffusion does not cause damage to the semiconductor surface, since there is no ion bombardment of the surface, and it is able to create very shallow and predictable charge concentration profiles.