A semiconductor device , comprising a layer sequence formed by a plurality of polar single crystalline semiconductor material layers that each have a crystal axis pointing in a direction that coincides with a direction of crystalline polarity and with a stacking direction of the layer sequence ; wherein - the layer sequence is formed by a core layer sequence and shell layer sequences (108.1, 108.2, 308.1, 308.2, 508.1, 508.2,808.1,808.2) on opposite sides of the core layer sequence in the stacking direction; and wherein the core layer sequence is formed by - an active region made of an active layer stack or a plurality of repetitions of the active layer stack, the active layer stack being formed by an active layer (104.1, 304.1, 504.1,1204.1) having a first material composition that is associated with a first band gap energy, and by carrier-confinement layers (104.2, 304.2, 304.3, 504.2a, 504.2b,1204.2) embedding the active layer (104.1, 304.1, 504.1,1204.1) on at least two opposite sides thereof and having a second material composition that is associated with a second band gap energy larger than the first band gap energy, wherein the active layer (104.1, 304.1, 504.1,1204.1) and the carrier-confinement layers (104.2, 304.2, 304.3, 504.2a, 504.2b,1204.2) are configured to effect a quantum-confinement of charge carriers in the active layer (104.1, 304.1, 504.1,1204.1) in one, two or three spatial dimensions; anc characterised in that the core layer sequence is further formed by - a pair of polarization guard layers (106.1, 106.2, 306.1, 306.2, 506.1, 506.2,1206.1,1206.2) adjacent to the active region and embedding the active region on opposite sides thereof, both polarization guard layers (106.1, 106.2, 306.1, 306.2, 506.1, 506.2,1206.1,1206.2) having the first material composition, and shielding the active layer(s) from internal polarization fields. - the layer sequence is formed by a core layer sequence and shell layer sequences (108.1, 108.2, 308.1, 308.2, 508.1, 508.2,808.1,808.2) on opposite sides of the core layer sequence in the stacking direction; and wherein the core layer sequence is formed by - an active region made of an active layer stack or a plurality of repetitions of the active layer stack, the active layer stack being formed by an active layer (104.1, 304.1, 504.1,1204.1) having a first material composition that is associated with a first band gap energy, and by carrier-confinement layers (104.2, 304.2, 304.3, 504.2a, 504.2b,1204.2) embedding the active layer (104.1, 304.1, 504.1,1204.1) on at least two opposite sides thereof and having a second material composition that is associated with a second band gap energy larger than the first band gap energy, wherein the active layer (104.1, 304.1, 504.1,1204.1) and the carrier-confinement layers (104.2, 304.2, 304.3, 504.2a, 504.2b,1204.2) are configured to effect a quantum-confinement of charge carriers in the active layer (104.1, 304.1, 504.1,1204.1) in one, two or three spatial dimensions; anc characterised in that the core layer sequence is further formed by - a pair of polarization guard layers (106.1, 106.2, 306.1, 306.2, 506.1, 506.2,1206.1,1206.2) adjacent to the active region and embedding the active region on opposite sides thereof, both polarization guard layers (106.1, 106.2, 306.1, 306.2, 506.1, 506.2,1206.1,1206.2) having the first material composition, and shielding the active layer(s) from internal polarization fields. <EOS>