Disclosure of Invention
The embodiment of the disclosure provides a growth method of an epitaxial wafer of a light emitting diode, which can improve the interface crystal quality of a quantum well layer and a quantum barrier layer, and further improve the light emitting efficiency of the light emitting diode. The technical scheme is as follows:
the embodiment of the disclosure provides a growth method of a light emitting diode epitaxial wafer, which comprises the following steps:
providing a substrate;
sequentially growing an N-type layer, an active layer and a P-type layer on the substrate, wherein the active layer comprises a plurality of InGaN quantum well layers and GaN quantum barrier layers which alternately grow in a period;
when each GaN quantum barrier layer of the active layer grows, discontinuously introducing hydrogen into the reaction cavity, continuously introducing nitrogen, controlling the flow of the introduced nitrogen to increase when the introduction of the hydrogen is stopped every time, and controlling the flow of the introduced nitrogen to decrease when the introduction of the hydrogen is stopped every time;
the growth temperature and the five-three ratio of each GaN quantum barrier layer during growth change from high to low for multiple times, and the growth rate gradually increases, then gradually decreases, then remains unchanged, and then gradually increases.
Optionally, the growth temperature of the GaN quantum barrier layer changes from high to low a times, a is larger than or equal to 2 and smaller than or equal to 5, the five-to-three ratio of the GaN quantum barrier layer changes from high to low b times, and b is larger than or equal to 2 and smaller than or equal to 5.
Optionally, the variation range of the growth rate of the GaN quantum barrier layer is 0.01-0.06 nm/s.
Optionally, the growth temperature of the GaN quantum barrier layer varies from 850 ℃ to 930 ℃.
Optionally, the variation range of the GaN quantum barrier layer is 20-60 ℃.
Optionally, when each GaN quantum barrier layer of the active layer grows, the flow rate of hydrogen introduced into the reaction chamber is 5-25L, and the variation range of the flow rate of introduced nitrogen is 40-100L.
Optionally, the variation range of the five-three ratio during growth of the GaN quantum barrier layer is 0.05-0.1.
Optionally, the variation range of the five-three ratio during growth of the GaN quantum barrier layer is 0.04-0.08.
Optionally, the growth time of the GaN quantum barrier layer is T, and the growth rate, the growth temperature, the flow of introduced hydrogen and nitrogen during growth, and the five-three ratio of the growth rate to the growth temperature of the GaN quantum barrier layer are controlled once every time T, wherein T is not less than 4T.
Alternatively, 10s ≦ t ≦ 50 s.
The technical scheme provided by the embodiment of the disclosure has the following beneficial effects:
and controlling the introduction of hydrogen and nitrogen when each GaN quantum barrier layer grows. Because the hydrogen and the In can react to influence the change of the In component, the hydrogen adopts a discontinuous introduction mode, which is equivalent to reducing the introduction of the hydrogen, and the influence of the hydrogen on the In the well layer can be reduced to a great extent. And when the hydrogen is stopped to be introduced, the introduction flow of the nitrogen is increased, and when the hydrogen is introduced, the introduction flow of the nitrogen is reduced, so that the uniformity of the GaN quantum barrier layer during growth is not influenced by the change of the airflow.
Further, the GaN quantum barrier layers alternately grow under the high-temperature and low-temperature environment, wherein the high-temperature growth can ensure the crystal quality of the grown GaN quantum barrier layers, and the precipitation of well layer In caused by the high-temperature growth of the barrier layers can be weakened during the low-temperature growth, so that the crystal quality of the GaN quantum barrier layers can be improved. And the growth at low temperature for many times can weaken the precipitation of In for many times, and the improvement effect on the barrier layer crystal quality is better. The five-to-three ratio of the GaN quantum barrier layer changes from high to low for multiple times, so that the growth of the GaN quantum barrier layer tends to a two-dimensional growth mode, defects such as N vacancies, large-size In-rich clusters and the like can be reduced, the crystal quality of the barrier layer can be further improved, the well barrier interface quality is improved, and the luminous efficiency of the LED is finally improved.
Further, In the initial stage of growth, the growth rate of the GaN quantum barrier layer is gradually increased firstly to rapidly transit to the growth of the barrier layer, so that the damage of the high temperature of the barrier layer to the well layer is reduced, and meanwhile, the negative influence of In segregation to the barrier layer can be weakened. And then, the growth rate is gradually reduced and kept unchanged, and the segregation of In the quantum well layer can be inhibited to a certain extent, so that micron-sized In-rich clusters are effectively reduced, the quality of the well barrier interface is improved, namely the well barrier interface is enabled to be clear, the limiting capability on carriers is improved, and the luminous efficiency of the LED is finally improved. Finally, the growth rate was again gradually increased for a fast transition to quantum well layer growth. On the one hand, the damage of the quantum well layer caused by high temperature can be reduced, and on the other hand, the production efficiency can also be improved.
The above parameters are changed together, so that the crystal quality of the barrier layer can be improved to the greatest extent, the definition of the trap barrier interface and the limiting capability of a current carrier are improved, and finally the luminous efficiency of the LED is greatly improved.
Detailed Description
To make the objects, technical solutions and advantages of the present disclosure more apparent, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
Fig. 1 is a flowchart of a method for growing a light emitting diode epitaxial wafer according to an embodiment of the present disclosure, where as shown in fig. 1, the method for growing includes:
step 101, a substrate is provided.
Wherein the substrate may be a sapphire substrate.
And 102, growing an N-type layer, an active layer and a P-type layer on the substrate in sequence.
The active layer comprises a plurality of InGaN quantum well layers and GaN quantum barrier layers which alternately grow in a periodic mode.
In step 102, for example, when each GaN quantum barrier layer of the active layer grows, hydrogen is intermittently introduced into the reaction chamber, nitrogen is continuously introduced, the flow rate of the introduced nitrogen is controlled to increase each time the introduction of hydrogen is stopped, and the flow rate of the introduced nitrogen is controlled to decrease each time the introduction of hydrogen is stopped.
The growth temperature and the five-three ratio of each GaN quantum barrier layer during growth change from high to low for multiple times, and the growth rate gradually increases, then gradually decreases, then remains unchanged, and then gradually increases.
In the embodiment of the disclosure, the thickness of each InGaN quantum well layer is 2 nm-4 nm, and the thickness of each GaN quantum barrier layer is 9 nm-20 nm.
In the embodiment of the disclosure, when each GaN quantum barrier layer grows, the introduction of hydrogen and nitrogen is controlled. Because the hydrogen and the In can react to influence the change of the In component, the hydrogen adopts a discontinuous introduction mode, which is equivalent to reducing the introduction of the hydrogen, and the influence of the hydrogen on the In the well layer can be reduced to a great extent. And when the hydrogen is stopped to be introduced, the introduction flow of the nitrogen is increased, and when the hydrogen is introduced, the introduction flow of the nitrogen is reduced, so that the uniformity of the GaN quantum barrier layer during growth is not influenced by the change of the airflow.
Further, the GaN quantum barrier layers alternately grow under the high-temperature and low-temperature environment, wherein the high-temperature growth can ensure the crystal quality of the grown GaN quantum barrier layers, and the precipitation of well layer In caused by the high-temperature growth of the barrier layers can be weakened during the low-temperature growth, so that the crystal quality of the GaN quantum barrier layers can be improved. And the growth at low temperature for many times can weaken the precipitation of In for many times, and the improvement effect on the barrier layer crystal quality is better. The five-to-three ratio of the GaN quantum barrier layer changes from high to low for multiple times, so that the growth of the GaN quantum barrier layer tends to a two-dimensional growth mode, defects such as N vacancies, large-size In-rich clusters and the like can be reduced, the crystal quality of the barrier layer can be further improved, the well barrier interface quality is improved, and the luminous efficiency of the LED is finally improved.
Further, In the initial stage of growth, the growth rate of the GaN quantum barrier layer is gradually increased firstly to rapidly transit to the growth of the barrier layer, so that the damage of the high temperature of the barrier layer to the well layer is reduced, and meanwhile, the negative influence of In segregation to the barrier layer can be weakened. And then, the growth rate is gradually reduced and kept unchanged, and the segregation of In the quantum well layer can be inhibited to a certain extent, so that micron-sized In-rich clusters are effectively reduced, the quality of the well barrier interface is improved, namely the well barrier interface is enabled to be clear, the limiting capability on carriers is improved, and the luminous efficiency of the LED is finally improved. Finally, the growth rate was again gradually increased for a fast transition to quantum well layer growth. On the one hand, the damage of the quantum well layer caused by high temperature can be reduced, and on the other hand, the production efficiency can also be improved.
The above parameters are changed together, so that the crystal quality of the barrier layer can be improved to the greatest extent, the definition of the trap barrier interface and the limiting capability of a current carrier are improved, and finally the luminous efficiency of the LED is greatly improved.
Fig. 2 is a flowchart of another growing method of an epitaxial wafer of a light emitting diode according to an embodiment of the present disclosure, and as shown in fig. 2, the growing method includes:
step 201, a substrate is provided.
The substrate can be a sapphire flat sheet substrate.
Further, step 201 may further include:
and processing the substrate at high temperature for 5-6 min in a hydrogen atmosphere. Wherein the temperature of the reaction chamber is 1000-1100 deg.C, and the pressure of the reaction chamber is controlled at 200-500 torr.
In this embodiment, a Veeco K465i or C4 or RB MOCVD (Metal Organic Chemical Vapor Deposition) apparatus is used to realize the epitaxial wafer growth method. By using high-purity H2(Hydrogen) or high purity N2(Nitrogen) or high purity H2And high purity N2The mixed gas of (2) is used as a carrier gas, high-purity NH3As an N source, trimethyl gallium (TMGa) and triethyl gallium (TEGa) as gallium sources, trimethyl indium (TMIn) as indium source, silane (SiH4) as an N-type dopant, i.e., Si source, trimethyl aluminum (TMAl) as aluminum source, and magnesium diclocide (CP) as aluminum source2Mg) as a P-type dopant, i.e., a Mg source. The pressure in the reaction chamber is 100to 600 torr.
Step 202, growing a low temperature buffer layer on the substrate.
Wherein, the low-temperature buffer layer is a GaN layer.
Illustratively, the temperature in the reaction chamber is controlled to be 530-560 ℃, the pressure is controlled to be 200-500 torr, and a low-temperature buffer layer with the thickness of 10-30 nm is grown on the [0001] surface of the sapphire.
Step 203, growing a high temperature buffer layer on the low temperature buffer layer.
Wherein, the high-temperature buffer layer is a GaN layer.
Illustratively, the temperature in the reaction chamber is controlled to be 1000-1100 ℃, the pressure is controlled to be 200-600 torr, and a high-temperature buffer layer with the thickness of 2-3.5 um is grown on the transition layer.
Step 204, growing an N-type layer on the high-temperature buffer layer.
Wherein, the N-type layer can be a GaN layer doped with Si.
Illustratively, the temperature in the reaction chamber is controlled to be 1000-1100 ℃, the pressure is controlled to be 150-300 torr, and an N-type layer with the thickness of 2-3 um is grown.
Step 205, an active layer is grown on the N-type layer.
The active layer comprises a plurality of InGaN well layers and GaN barrier layers which are alternately grown in a period. The number of active layers may be 5 to 11.
Illustratively, step 205 includes:
when each GaN quantum barrier layer of the active layer grows, hydrogen is discontinuously introduced into the reaction cavity, nitrogen is continuously introduced, the flow of the introduced nitrogen is controlled to increase when the introduction of the hydrogen is stopped every time, and the flow of the introduced nitrogen is controlled to decrease when the introduction of the hydrogen is stopped every time.
The growth temperature and the five-three ratio of each GaN quantum barrier layer during growth change from high to low for multiple times, and the growth rate gradually increases, then gradually decreases, then remains unchanged, and then gradually increases.
Optionally, the growth temperature of the GaN quantum barrier layer changes from high to low a times, a is larger than or equal to 2 and smaller than or equal to 5, the five-to-three ratio of the GaN quantum barrier layer changes from high to low b times, and b is larger than or equal to 2 and smaller than or equal to 5.
If the number of a is less than 2, the effect of reducing the precipitation of In the well layer and improving the crystal quality of the barrier layer can be achieved because the number of low-temperature changes is small. If the number of a is more than 5, the production efficiency of the LED is increased due to more temperature change times, and the cost is increased.
Optionally, the variation range of the growth rate of the GaN quantum barrier layer is 0.01-0.06 nm/s.
If the growth rate is less than 0.01nm/s, the production efficiency is affected because the growth rate is too slow. If the growth rate is greater than 0.06nm/s, the formation of a clear well-barrier interface is affected because the growth rate is faster.
Illustratively, the growth rate of the GaN quantum barrier layer varies from 0.02 nm/s to 0.04 nm/s.
Optionally, the growth rate of the GaN quantum barrier layer is 1.5-6 times that of the InGaN quantum well layer.
If the growth rate of the barrier layer is lower than 1.5 times of the growth rate of the well layer, the overall production efficiency is affected because the growth rate of the barrier layer is low. If the growth rate of the barrier layer is 6 times higher than that of the well layer, the crystal quality of the barrier layer and the definition of the well-barrier transition interface are affected due to the fact that the growth rate of the barrier layer is too high.
Illustratively, the growth rate of the GaN quantum barrier layer is 1.5-4 times that of the InGaN quantum well layer.
Optionally, the growth temperature of the GaN quantum barrier layer varies from 850 ℃ to 930 ℃.
If the growth temperature of the GaN quantum barrier layer is lower than 850 ℃, the crystal quality of the whole quantum barrier layer is affected due to the lower temperature, and if the growth temperature of the GaN quantum barrier layer is higher than 930 ℃, although the crystal quality of the whole quantum well can be greatly improved, the InGaN quantum well layer can be seriously damaged (for example, In the InGaN quantum well layer is separated out).
Optionally, the variation range of the GaN quantum barrier layer is 20-60 ℃.
If the temperature is lower than 20 ℃, the crystal quality of the barrier layer is affected by the temperature difference. If the temperature is higher than 60 ℃, the temperature difference is too large, and the temperature of the barrier layer is too high, so that the crystal quality of the well layer is damaged.
Illustratively, the variation amplitude of the GaN quantum barrier layer is 30-50 ℃.
Optionally, when each GaN quantum barrier layer of the active layer grows, the flow rate of hydrogen introduced into the reaction chamber is 5-25L, and the variation range of the flow rate of introduced nitrogen is 40-100L.
If the flow rate of the introduced hydrogen is lower than 5L, the change amplitude of the barrier layer growth rate is small, and if the flow rate of the introduced hydrogen is higher than 25L, H is caused2The amount is large to affect the In composition stability of the well layer.
If the flow of the introduced nitrogen is lower than 40L, the whole gas quantity is less, and then the gas flow distribution of the whole quantum barrier layer is influenced, and if the flow of the introduced nitrogen is higher than 100L, the influence of the whole MO source concentration is greater, and then the thickness, the light intensity and other parameters of the active layer are influenced.
Optionally, the ratio of the flow rates of the introduced nitrogen and the hydrogen is 5-20.
If the ratio is less than 5, the stability of the In component In the quantum well is affected due to the use of a large amount of hydrogen. If the ratio is larger than 20, the crystal quality of the barrier layer is further improved and the definition of In pair well barrier interface formation is reduced due to the fact that the hydrogen consumption is small.
Optionally, the variation range of the five-three ratio during growth of the GaN quantum barrier layer is 0.05-0.1.
If the five-to-three ratio of the GaN quantum barrier layer is less than 0.05 during growth, two-dimensional growth is weakened. If the five-three ratio of the GaN quantum barrier layer is greater than 0.1 during growth, the thickness of the whole quantum barrier layer is reduced, and the photoelectric performance is affected.
Wherein, the five-three ratio refers to the mol ratio of the group V source and the group III source which are introduced into the reaction cavity.
Optionally, the variation range of the five-three ratio during growth of the GaN quantum barrier layer is 0.04-0.08.
If the variation range is less than 0.04, the two-dimensional growth mode formation is affected because the variation value of the five-three ratio is small. If the variation amplitude is larger than 0.08, the light emitting efficiency of the LED under low current is also influenced because the five-three ratio is greatly changed.
Illustratively, the variation amplitude of the five-three ratio of the GaN quantum barrier layer is 0.06-0.08.
Optionally, the growth time of the GaN quantum barrier layer is T, and the growth rate, the growth temperature, the flow of introduced hydrogen and nitrogen during growth, and the five-three ratio change once every time T, wherein T is not less than 4T, so as to facilitate actual growth control.
Alternatively, 10s ≦ t ≦ 50 s.
Fig. 3 is a schematic diagram illustrating a change in growth rate of a GaN quantum barrier layer according to an embodiment of the present disclosure, as shown in fig. 3, the growth rate of the GaN quantum barrier layer gradually increases in a time period from 0to t1, and the growth rate of the GaN quantum barrier layer gradually decreases in a time period from t1 to t 2. The growth rate of the GaN quantum barrier layer is kept unchanged in the time period from t2 to t3, and the growth rate of the GaN quantum barrier layer is gradually increased in the time period from t3 to t 4.
Fig. 4 is a schematic diagram illustrating a change in growth temperature of a GaN quantum barrier layer according to an embodiment of the present disclosure, as shown in fig. 4, the growth temperature of the GaN quantum barrier layer gradually increases in a time period from 0to t1, and the growth temperature of the GaN quantum barrier layer gradually decreases in a time period from t1 to t 2. In the time period from t2 to t3, the growth temperature of the GaN quantum barrier layer gradually increases, and in the time period from t3 to t4, the growth temperature of the GaN quantum barrier layer gradually decreases.
Fig. 5 is a schematic diagram illustrating a change in flow rate of hydrogen provided by an embodiment of the disclosure, as shown in fig. 5, hydrogen is introduced into the reaction chamber during a time period from 0to t1, and the introduction of hydrogen into the reaction chamber is stopped during a time period from t1 to t 2. And introducing hydrogen into the reaction cavity in the time period from t2 to t3, and stopping introducing the hydrogen into the reaction cavity in the time period from t3 to t 4.
Fig. 6 is a schematic diagram illustrating a change in flow rate of nitrogen provided by an embodiment of the disclosure, as shown in fig. 6, the flow rate of nitrogen gradually decreases in a time period from 0to t1, and the flow rate of nitrogen gradually increases in a time period from t1 to t 2. The flow rate of nitrogen was gradually decreased during the period from t2 to t3, and gradually increased during the period from t3 to t 4.
Fig. 7 is a schematic diagram illustrating a variation of the five-three ratio during growth of the GaN quantum barrier layer according to the embodiment of the disclosure, as shown in fig. 7, the five-three ratio during growth of the GaN quantum barrier layer gradually increases in a time period from 0to t1, and the five-three ratio during growth of the GaN quantum barrier layer gradually decreases in a time period from t1 to t 2. In the time period from t2 to t3, the five-three ratio of the GaN quantum barrier layer during growth gradually increases, and in the time period from t3 to t4, the five-three ratio of the GaN quantum barrier layer during growth gradually decreases.
Wherein the time intervals of the time period 0to t1, the time period t1 to t2, the time period t2 to t3 and the time period t3 to t4 are all t.
In the above embodiment, for example, the growth time of each GaN quantum barrier layer is 60s, t is 15s, that is, the growth rate, the growth temperature, the flow rates of the hydrogen and nitrogen introduced during growth, and the ratio of five to three are controlled once every 15 s. And the growth rate and the growth temperature of the quantum barrier layer, the flow of introduced hydrogen and nitrogen during growth and five-three ratio change are controlled for three times, so that the growth of a GaN quantum barrier layer can be completed.
Optionally, the thickness of each GaN quantum barrier layer is 9nm to 20 nm.
Optionally, each InGaN quantum well layer has a thickness of 2nm to 4 nm.
Illustratively, step 205 further comprises:
controlling the temperature in the reaction cavity to be 760-780 ℃, controlling the pressure to be 200torr, and growing the InGaN quantum well layer with the thickness of 2-4 nm.
Step 206, an electron blocking layer is grown on the active layer.
Wherein the electron blocking layer is Mg-doped AlyGa1-yN(y=0.15~0.25)。
Illustratively, the temperature in the reaction cavity is controlled to be 930-970 ℃, the pressure is controlled to be 100torr, and the electron blocking layer with the thickness of 30-50 nm is grown on the active layer.
Step 207, a P-type layer is grown on the electron blocking layer.
Wherein the P-type layer is a Mg-doped GaN layer, and the doping concentration of Mg is 8 x 1018cm-3~6*1019cm-3。
Illustratively, the temperature in the reaction cavity is controlled to be 940-980 ℃, the pressure is controlled to be 200-600 torr, and a P-type layer with the thickness of 50-80 nm is grown on the electron blocking layer.
In the embodiment of the disclosure, when each GaN quantum barrier layer grows, the introduction of hydrogen and nitrogen is controlled. Because the hydrogen and the In can react to influence the change of the In component, the hydrogen adopts a discontinuous introduction mode, which is equivalent to reducing the introduction of the hydrogen, and the influence of the hydrogen on the In the well layer can be reduced to a great extent. And when the hydrogen is stopped to be introduced, the introduction flow of the nitrogen is increased, and when the hydrogen is introduced, the introduction flow of the nitrogen is reduced, so that the uniformity of the GaN quantum barrier layer during growth is not influenced by the change of the airflow.
Further, the GaN quantum barrier layers alternately grow under the high-temperature and low-temperature environment, wherein the high-temperature growth can ensure the crystal quality of the grown GaN quantum barrier layers, and the precipitation of well layer In caused by the high-temperature growth of the barrier layers can be weakened during the low-temperature growth, so that the crystal quality of the GaN quantum barrier layers can be improved. And the growth at low temperature for many times can weaken the precipitation of In for many times, and the improvement effect on the barrier layer crystal quality is better. The five-to-three ratio of the GaN quantum barrier layer changes from high to low for multiple times, so that the growth of the GaN quantum barrier layer tends to a two-dimensional growth mode, defects such as N vacancies, large-size In-rich clusters and the like can be reduced, the crystal quality of the barrier layer can be further improved, the well barrier interface quality is improved, and the luminous efficiency of the LED is finally improved.
Further, In the initial stage of growth, the growth rate of the GaN quantum barrier layer is gradually increased firstly to rapidly transit to the growth of the barrier layer, so that the damage of the high temperature of the barrier layer to the well layer is reduced, and meanwhile, the negative influence of In segregation to the barrier layer can be weakened. And then, the growth rate is gradually reduced and kept unchanged, and the segregation of In the quantum well layer can be inhibited to a certain extent, so that micron-sized In-rich clusters are effectively reduced, the quality of the well barrier interface is improved, namely the well barrier interface is enabled to be clear, the limiting capability on carriers is improved, and the luminous efficiency of the LED is finally improved. Finally, the growth rate was again gradually increased for a fast transition to quantum well layer growth. On the one hand, the damage of the quantum well layer caused by high temperature can be reduced, and on the other hand, the production efficiency can also be improved.
The above parameters are changed together, so that the crystal quality of the barrier layer can be improved to the greatest extent, the definition of the trap barrier interface and the limiting capability of a current carrier are improved, and finally the luminous efficiency of the LED is greatly improved.
The above description is intended to be exemplary only and not to limit the present disclosure, and any modification, equivalent replacement, or improvement made without departing from the spirit and scope of the present disclosure is to be considered as the same as the present disclosure.