A monolithic three-dimensional memory device comprising: a stack of alternating layers comprising insulating layers and electrically conductive layers and located over a substrate; a memory opening vertically extending through the stack of alternating layers; a memory film located on the sidewalls of the memory opening; a semiconductor channel (512, 514) extending through the memory opening and located over the memory film and comprising: a first semiconductor material layer having a first band gap and located over the memory film; and a second semiconductor material layer having a second band gap that is narrower than the first band gap and located over the first semiconductor material layer, wherein a two-dimensional electron gas for electrical current conduction is present at, or in proximity to, an interface between the first semiconductor material layer and the second semiconductor material layer, characterised in that: the first semiconductor material layer comprises a first III-V compound semiconductor material; and the second semiconductor material layer comprises a second III-V compound semiconductor material different from the first III-V compound semiconductor material. a stack of alternating layers comprising insulating layers and electrically conductive layers and located over a substrate; a memory opening vertically extending through the stack of alternating layers; a memory film located on the sidewalls of the memory opening; a semiconductor channel (512, 514) extending through the memory opening and located over the memory film and comprising: a first semiconductor material layer having a first band gap and located over the memory film; and a second semiconductor material layer having a second band gap that is narrower than the first band gap and located over the first semiconductor material layer, wherein a two-dimensional electron gas for electrical current conduction is present at, or in proximity to, an interface between the first semiconductor material layer and the second semiconductor material layer, characterised in that: the first semiconductor material layer comprises a first III-V compound semiconductor material; and the second semiconductor material layer comprises a second III-V compound semiconductor material different from the first III-V compound semiconductor material. a first semiconductor material layer having a first band gap and located over the memory film; and a second semiconductor material layer having a second band gap that is narrower than the first band gap and located over the first semiconductor material layer, wherein a two-dimensional electron gas for electrical current conduction is present at, or in proximity to, an interface between the first semiconductor material layer and the second semiconductor material layer, characterised in that: the first semiconductor material layer comprises a first III-V compound semiconductor material; and the second semiconductor material layer comprises a second III-V compound semiconductor material different from the first III-V compound semiconductor material. the first semiconductor material layer comprises a first III-V compound semiconductor material; and the second semiconductor material layer comprises a second III-V compound semiconductor material different from the first III-V compound semiconductor material.