Two of the pairings are definitional and settle the code: (A)-(IV), (B)-(I), (C)-(II), (D)-(III), option 1.

(C) Transferred electron device and InP. A transferred-electron device is the Gunn diode, and it works only in materials whose conduction band has a low-mass central valley and higher-lying satellite valleys. At a high enough field, electrons are transferred from the light valley to the heavy one, where their mobility is far lower — so the drift velocity falls as the field rises:

\(\dfrac{dv}{dE}\lt0\)

That negative differential mobility makes domains of space charge form and travel, producing oscillation at the transit frequency \(f=v/L\). Only a few materials have the required band structure, and GaAs and InP are the two used — silicon cannot do it at all.

(D) Avalanche transit time device and the Read diode. The IMPATT family exploits two delays that together give a 180° phase shift between voltage and current: the avalanche build-up lags the field by 90°, and the transit of the generated carriers across a drift region adds another 90°. The result is negative resistance at microwave frequencies. W. T. Read proposed the original n⁺-p-i-p⁺ structure in 1958, and the Read diode is its name.

(A) Microwave transistor and HBT. A heterojunction bipolar transistor uses a wide-gap emitter, which blocks hole back-injection from base to emitter and so keeps the injection efficiency high even with a heavily doped base. Heavy base doping means low base resistance and a very thin base, so both the transit time and the RC delay fall — which is what makes the HBT the standard microwave bipolar device.

(B) Field effect transistor and CCD. The remaining pairing, taken by elimination. Both are surface field-effect structures on a MOS foundation: a CCD is a chain of MOS gates in which the surface potential well is controlled by the gate voltage, exactly as in a field-effect transistor.

The quickest route : InP can only belong to the transferred-electron entry, since that is the material class the effect requires, and "Read diode" can only be the avalanche transit-time device. Those two alone leave option 1.

Hence, the correct code is (A)-(IV), (B)-(I), (C)-(II), (D)-(III).