Influence of growth temperature and growth rate of p-GaN layers on the characteristics of green light emitting diodes

Abstract

We investigated the electrical and structural qualities of Mg-doped p-type GaN layers grown under different growth conditions by metalorganic chemical vapor deposition (MOCVD). Lower 300 K free-hole concentrations and rough surfaces were observed by reducing the growth temperature from 1,040 o C to 930 o C. The hole concentration, mobility, and electrical resistivity were improved slightly for Mg-doped GaN layers grown at 930 o C with a lower growth rate, and also an improved surface morphology was observed. In 0.25 Ga 0.75 N/GaN multiple-quantum-well light emitting diodes (LEDs) with p-GaN layers grown under different conditions were also studied. It was found from photoluminescence studies that the optical and structural properties of the multiple quantum wells in the LED structure were improved by reducing the growth temperature of the p-layer due to a reduced detrimental thermal annealing effect of the active region during the GaN:Mg p-layer growth. No significant difference in the photoluminescence intensity depending on the growth time of the p-GaN layer was observed. However, it was also found that the electroluminescence (EL) intensity was higher for LEDs having p-GaN layers with a lower growth rate. Further improvement of the p-GaN layer crystalline and structural quality may be required for the optimization of the EL properties of long-wavelength (;540 nm) green LEDs.

The Effect of Imbalanced Carrier Transport on the Efficiency Droop in GaInN-Based Blue and Green Light-Emitting Diodes

“…Energies 2017, 10, 1277 3 of 8 and 7.5 × 10 17 cm −3 and 8 cm 2 /(V•s) in p-type GaN grown at 950 °C, respectively [22,23]. Light outputcurrent-voltage (L-I-V) characteristics for top-emitting packaged blue and green LEDs were measured at temperatures ranging from 80 to 300 K by using a vacuum chamber probe station equipped with an Agilent B2902 precision source-measurement unit.…”

“…Assuming an electron concentration of n = 2 × 10 18 cm −3 and an electron mobility of 150 cm 2 /(V•s), which are typical values for conventional n-type GaN [24], allows us to calculate an n-to-p "asymmetry factor" that can be defined as the ratio of conductivities, σn/σp. Using the abovementioned hole transport characteristics for epitaxial GaN grown at 1050 °C (blue LEDs) and 950 °C (green LEDs), the asymmetry factor (σn/σp) has a value of 17.1 for blue LEDs but a value of 50.1 for green LEDs, illustrating the more strongly imbalanced n-to-p transport characteristics of green LEDs [22]. Figure 1 shows a comparison of the asymmetry of n-to-p transport characteristics of blue and green LEDs.…”

“…For such a difference in wavelength (450 nm versus 520 nm), the In mole fraction in the quantum wells of the green LEDs was~22%, i.e., higher than in those of the blue LEDs,~14%, which was enabled by reducing the growth temperature for the active region and subsequent p-type layers (1050 • C and 950 • C for the blue and green LEDs, respectively). The typical values of hole concentration and mobility were about 1.1 × 10 18 cm −3 and 16 cm 2 /(V·s) in p-type GaN grown at 1050 • C, and 7.5 × 10 17 cm −3 and 8 cm 2 /(V·s) in p-type GaN grown at 950 • C, respectively [22,23]. Light output-current-voltage (L-I-V) characteristics for top-emitting packaged blue and green LEDs were measured at temperatures ranging from 80 to 300 K by using a vacuum chamber probe station equipped with an Agilent B2902 precision source-measurement unit.…”

Internal quantum efficiency improvement of InGaN/GaN multiple quantum well green light-emitting diodes

“…The ther− mal damage of the InGaN/GaN MQW, which is caused by high growth temperature of p−GaN, is attributed to the in− dium diffusion into GaN barrier layers from InGaN well layers [20]. It's promising to reduce the growth temperature of a p−GaN layer for better optical and structural properties of InGaN/GaN MQW [21]. The quality of InGaN/GaN MQW green LED could also be improved by "active−re− gion−friendly" p−InGaN layers grown at low temperature [22][23][24].…”

Characteristics of Green Light-Emitting Diodes Using an InGaN:Mg/GaN:Mg Superlattice as p-Type Hole Injection and Contact Layers

“…This detrimental annealing effect will be more significant in green LEDs, the active region of which contains higher In composition (In $ 20% to 30%) and thus needs to be grown at much lower temperatures than p-GaN:Mg layers. The authors have investigated the effect of thermal annealing induced by p-type layers grown under different growth conditions on photoluminescence (PL) properties of the active region, 5 and have compared the degradation behavior of the active region for both green and blue LEDs depending on the p-GaN:Mg growth conditions. 6 It was found that the optical quality degradation of the green LED active region is significant, while that of the blue LED active region is negligible, both with p-GaN:Mg grown at 930°C.…”