Abstract
The development of the modified Read Lo‐Hi‐Lo high efficiency 
IMPATT requires special growth techniques permitting controlled growth of thin (100–1000Å) layers containing specified amounts of n‐type impurities with high accuracy. To meet this need a gas dopant injection system compatible with standard CVD apparatus was constructed. An accurately measured total amount of 
for doping the n+ layer is instantaneously released into the gas stream passing over the growing epitaxial layer and is partially incorporated in that layer. The control exercised over parameters of the n+ layers was: the width, ±8%; the position, ±10%; and the impurity content, ±18%. It is shown that the width of a sulfur‐doped layer is determined by (i) the experimental geometry, (ii) gas flow rates, (iii) gaseous diffusion, and (iv) growth rate. The incorporation of sulfur is shown to be proportional to the number of moles of 
injected and varies as the (growth rate)1.6. Studies of postgrowth diffusion in the solid indicate that the widths of the high‐doped layers broaden by amounts consistent with a value for the diffusion coefficient of sulfur in
of
The doping technique has yielded the first experimental measurement of a distribution coefficient of sulfur between the gas and the solid phases. This distribution coefficient is defined as
and has a value ranging between 13 and 26 for our experimental conditions. This study has shown that the injection doping system allows control of the concentration of impurities via the ideal gas law in layers as thin as 150Å. It has furthermore been demonstrated that growth rate control is of primary importance for doping control and that future studies to improve doping control should focus on the variables affecting growth rates.