Fig. 1. The shapes of gradient doping structure. (a) Linear gradient doping. (b) Exponential gradient doping. (c) Logarithmic gradient doping. (d) Smooth gradient doping.

Fig. 2. (Color online) Structures of GaAs LPCs with different position of gradient doping region.

Fig. 3. Distribution of recombination rate in traditional structure of GaAs LPCs.

Fig. 4. (Color online) Simulation results of the base layer of linear gradient doping LPC. (a) Simulation about doping concentration when the gradient doping region thickness (GDT) in base layer is 1.5, 2.5, and 3.5 μm. (b) Simulation about the thickness of gradient doping region.

Fig. 5. (Color online) (a) Distribution of electric field in base layer with different front surface doping concentration. (b) Distribution of recombination rate in base layer with different front surface doping concentration.

Fig. 6. (Color online) Simulation results of the emitter layer of linear gradient doping LPC. (a) Simulation about doping concentration when the entire emitter layer is doped gradually. (b) Simulation about the thickness of gradient doping region in different position.

Fig. 7. Simulation about doping concentration on the (a) back and (b) front surface of the gradient doping region in base layer. Simulation about doping concentration on the (c) front and (d) back surface of the gradient doping region in emitter layer.

Fig. 8. (Color online) Simulation results of the base layer of exponential gradient doping LPC. (a) Simulation about doping concentration when the entire base layer is doped gradually. (b) Simulation about the thickness of gradient doping region

Fig. 9. (Color online) Simulation results of the emitter layer of exponential gradient doping LPC. (a) Simulation about doping concentration when the entire emitter layer is doped gradually. (b) Simulation about the thickness of gradient doping region in different position.

Fig. 10. (Color online) (a) Distribution of electric field in base layer of linear and exponential gradient doping LPCs. (b) Distribution of recombination rate in base layer of linear and exponential gradient doping LPCs.