PHOTO-HALL STUDIES OF MODULATION-DOPED FIELD-EFFECT TRANSISTOR HETEROSTRUCTURES USING (INAS)(M)(GAAS)(N) SUPERLATTICE CHANNELS

We studied the electrical properties, the Hall mobility and the free c arrier concentration of modulation-doped field-effect transitor hetero structures using M(InAs)(m)N(GaAs)(n) short-period superlattice (SPS) channels. We changed the number of monolayers m for InAs, n for GaAs a nd the numbers M and N of interfaces InAsm-GaAsn in the channel. In th e SPS, the thickness of the InAs layer was varied from 0.5 +/- 0.1 to 1.6 +/- 0.1 monolayers (ML) and that of GaAs from 5 to 15 ML. The numb er M of interfaces varied from 3 to 7 while the number N varied from 2 to 6. The total SPS channel thickness was varied, but always kept bel ow the critical layer thickness calculated from the double kink model derived by Matthews and Blakeslee. The persistent photoconductivity ef fect, at 77 K, was employed to study the variation of the Hall mobilit y and free carrier density in the SPS channels. A red light-emitting d iode was used as the illumination source. Our results indicate that th e Hall mobility increases for (a) a decreasing number of InAs-GaAs and GaAs-InAs interfaces, (b) on employing an integral number of InAs mon olayers, and (c) on employing an increasing number of GaAs monolayers. We believe that they are effective in producing surface smoothing.