Integral packaging for millimetre-wave GaAs IMPATT diodes prepared by molecular beam epitaxy

An 'integrating packaging' technique developed to package high-frequency, double-drift GaAs diodes fabricated from wafers prepared by molecular beam epitaxy is described. All the devices are tested in microstrip resonator circuits. CW and pulse oscillations up to 109 GHz are obtained. Instead of thinning the raw substrate by mechanical lapping after growth, the need for a very thin substrate is met by replacing the raw substrate by an effective substrate that is an epitaxially grown n(+) GaAs buffer layer of any thickness desired. To facilitate subsequent detachment of the raw substrate from the n(+) buffer and active layers, an epitaxial Al(x)Ga(1-x)As layer is grown between the substrate and the buffer layer to serve as an etch-stop layer. In this way, the raw substrate and the etch-stop layer, which are of different chemical compositions, can be removed in sequence with selective chemical etching.