Making an OC604 Spez

Making a OC604 Spez Transistor

Translated from Röhren Dokument Nr 3

I The germanium n-type wafer of the germanium OC604 spez (medium power transistor) shown in the picture below is 2.7x2.7 mm and is 0.2mm or 200μ thick. The indium collector dot visible in the picture is approximately 1.7mm in diameter.

OC604 Spez (courtesy Andrew Wylie)

II The n-type germanium layer between the p-layers is only 40 … 60 μ thick (Bild 2). Since the thickness of this layer is of crucial importance to the magnitude of the current gain the extent of the indium alloying must be controlled very precisely.

III The n-germanium must contain a precisely defined number of impurity atom (arsenic or antimony), and the desired resistivity is obtained with between 1 to 10⁸ and 10⁷ germanium atoms.

Whence:

ρ ≈ 7.0 Ω cm (at 10⁸: 1)

ρ ≈ 0.7 Ω cm (at 10⁷: 1)

(Note in this case ρ refers to a 1cm cube and with a cross-section of 1cm² and not as is more usual, a wire 1m long with a cross-section 1mm²)

IV In this case the original germanium has a purity of 10^-9, ie in 10¹¹ germanium atoms there is only one impurity atom.

This level of purity is equivalent to doing nothing but throwing a bean in a pot every second for 31 years and making a mistake only once by throwing in a pea instead.

V A cubic centimetre of germanium ie a germanium cube of the size shown adjacentweighing only 5.25 grams contains 4.3x10²² atoms.

Just imagine if an atom were the size of a grain of wheat, then the surface of a sphere the size of the Earth would be covered with wheat grains 2m high.