“…Metamorphic devices which have been fabricated on lattice-mismatched substrates include InGaAs/InAlAs HEMTs on GaAs, 3 InGaAs/InAlAs heterojunction bipolar transistors (HBTs) on GaAs, 4 InGaAs/InP HEMTs and HBTs on GaAs, 5 InAlAs photodiodes on GaAs, 6 InAsSb/AlInAsSb light-emitting diodes (LEDs) on GaSb, 7 AlInGaAsSb laser diodes on GaSb, 8 InGaAs/InAlGaAs laser diodes on GaAs, 9 InGaAsSb/InAlAs quantum cascade laser structures on GaAs, 10 and InAlAs solar cells on GaAs. 11 Most work has focused on linearly-graded buffer layers, [2][3][4][5][6][7][8][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] while there have been several reports of the use of step-graded buffer layers 12,[31][32][33][34] or buffer layers with T. Kujofsa continuous, but non-linear grading of composition. 11,[35][36][37] Tersoff's work …”