Delta-doping superlattices in multiple quantum wells

The quantum confined Stark effect has been extensively used for amplitude m odulation. One way of improving the performance of multiple quantum well st ructures to be used in light modulation at high bit rates is by increasing the Stark shift for a given externally applied voltage. GaAs/AlGaAs multipl e quantum well structures containing an nipi delta-doping superlattice, whe re the n-type doping is inserted in the quantum wells and the p-type in the barriers, are expected to double the Stark shift, according to Batty and A lsopp (Electron. Lett. 29 (1993) 2066). Such structures have been studied i n detail to evaluate their potential for use in the fabrication of optical modulators. It has been observed that the required balance between n- and p -type doping levels is not trivial to achieve due to the presence of interf ace hole traps whose population depends on the quantum well doping concentr ation. It is estimated that for undoped quantum wells around 15% of the hol es provided by the p-doping are trapped at the interfaces. Photo luminescen ce measurements, supported by calculations, point out that even though an i ndirect transition between electrons in the quantum wells and holes in the barriers is present at low temperatures at energies below the quantum well fundamental transition energy, at room temperature such a transition is abs ent and the observed optical emission occurs at essentially the same energy as that of an equivalent undoped structure. (C) 2001 Elsevier Science B.V. All rights reserved.