KR100266067B1 - Plasma annealing method for p-type activation of mg-doped gan semiconductor films grown by mocvd - Google Patents

Abstract

The present invention relates to a p-type activation method for activating a semiconductor thin film of gallium nitride by doping a p-type impurity, the first step of growing a GaN buffer layer on a sapphire substrate at a constant height and temperature by an organometallic chemical vapor deposition method And a second process of growing a GaN thin film doped with magnesium into the GaN buffer layer at a high temperature at a constant thickness, and using nitrogen gas as the main flow during the second process, and nitrogen in a vacuum vessel of 10 ^-3 Torr. B) a third step of annealing with an argon plasma.

As described above, according to the present invention, instead of using hydrogen gas or hydrogen / nitrogen mixed gas as the main mixed gas in the reactor, nitrogen gas is used to suppress the formation of Mg-H composite due to decomposition of hydrogen gas during thin film growth. In addition, the plasma annealing provides an effect of realizing p-type with a high carrier concentration which can further reduce the amount of hydrogen.

Description

Plasma Activation Method of Magnesium-doped Gallium Nitride Thin Film Grown by Organometallic Chemical Vapor Deposition by Plasma Annealing

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a p-type activation method for activating a semiconductor thin film of gallium nitride by doping a p-type impurity. Particularly, the present invention relates to annealing plasma by using a main stream gas of nitrogen gas during crystal growth. The present invention relates to a p-type activation method by plasma annealing of a magnesium-doped gallium nitride-based thin film grown by organometallic chemical vapor deposition to enable p-type activation.

In particular, when the main flow gas source during crystal growth is hydrogen, hydrogen / nitrogen mixed gas or nitrogen gas, p-type activation is affected. To this end, the present invention provides a method of optical activation by irradiating ultraviolet rays to a substrate during thin film growth with a nitrogen gas source or a small amount of silicon (Si) or zinc (Zn) in magnesium (Mg) as a doping gas. Including a method of using a codoping organometallic source, p-type activation is possible, and a good quality p-type gallium nitride layer can be grown.

Recently, optoelectronic devices of gallium nitride-based semiconductors have been applied to spectral regions of blue and ultraviolet rays.

One of the important problems in this application is the p-type activation of gallium nitride. The main growth method of gallium nitride is chemical vapor deposition (MOCVD) using an organometallic source, and magnesium is used as a p-type acceptor dopant.

However, the magnesium acceptor easily bonds with the hydrogen atom and is enclosed, thereby compensating for the hole without having a p-type. Efforts have been made to overcome these physical phenomena, particularly the method of desorption of hydrogen (LEEBI) by irradiating low energy electron beam after growing gallium nitride (LEEBI) and the method of thermal annealing in nitrogen atmosphere after growth. Designed.

Doping Zn (zinc) or Mg (magnesium) with p-type impurities during thin film growth of other III-V semiconductor materials, GaAs, GaP, InP, etc., produces p-type, but not for GaN thin films. not. Even if the p-type impurity is added, the p-type of low resistance is not formed, and an insulating layer having a high dielectric constant of high resistance is obtained.

When the electron beam is irradiated on the grown thin film, magnesium is not placed in the Ga (gallium) position immediately after growth in the GaN crystal added with magnesium, and thus the magnesium does not act as an acceptor. The p-formation was analyzed by moving the magnesium into the Ga position. This interpretation has been reinterpreted.

It was also found that p-type activation was caused by the thermal energy at the thin film surface by electron beams, and the same effect was obtained by increasing the GaN temperature in vacuum or nitrogen atmosphere. The interpretation of this p-formation mechanism was understood to be due to the fact that hydrogen gas forms Mg-H complexes during the reaction rather than the magnesium atoms move to the Ga position due to the weak thermal energy.

The hydrogen bonding is different from that of other III-V semiconductors, and the gas used in the vapor deposition method is ammonia gas and the ammonia gas is interpreted as the main reason only because the growth temperature is different. Hydrogen atoms decomposed above ℃ were entered into the Ga position and combined with magnesium in the Ga position to form a Mg-H complex and was understood to provide a cause of high resistance p-type inactivation.

More specifically, on the sapphire substrate, a GaN thin film layer was first grown on a sapphire substrate with a buffer layer of 0.02-0.05 μm of AlN (aluminum) at a low temperature of about 400-600 ° C. and then doped with magnesium at a high temperature of about 1000 ° C. When p-type was formed by irradiating electron beams on the surface, the hole carrier concentration was up to 10 ¹⁷ / cm3 and the p-type was successfully lowered to 12 _Ω (Ohm: Greeks) -cm. Further development, when forming a 0.04 ㎛ GaN buffer layer and a 4 ㎛ GaN thin film layer doped with 10 ²⁰ / cm 3 doped with magnesium as a p-type impurity on the substrate first when the heat treatment at 700 ℃ up to 3-5 × 10 ¹⁷ / cm 3 It realized the resistance of the positive hole carrier concentration and a minimum 2 _Ω -㎝.

However, these interpretations differ in the method of supplying the energy required for the activation of the Mg-H complex and the activation rate is very low. In addition, an energy supply method capable of activating a hydrogenated acceptor with high efficiency is required, and when the p-plane electrode is formed at the p-GaN / metal interface due to low activation, it causes a high ohmic resistance and a high load voltage (Vf) and It causes a problem of limiting the performance in manufacturing the optoelectronic device, such as lowering the luminous efficiency (Po).

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and its object is to grow a p-type gallium nitride thin film to re-analyze the p-type activation mechanism to improve p-type activation rate and high hole carrier concentration. It is to provide a p-type activation method to have a.

More specifically, by using nitrogen gas instead of using hydrogen gas or hydrogen / nitrogen mixed gas as the main mixed gas in the reactor, p-type formation is suppressed by suppressing the formation of Mg-H composite without energy by subsequent heat treatment after thin film growth. And the binding energy required for the formation of the complex because the hydrogen atom and the magnesium atom from the organometallic source and the ammonia gas can react to form the Mg-H complex during the crystal growth using the main flow gas as the nitrogen gas. Is excited by light energy using the ultraviolet spectrum at the growth surface to desorb hydrogen atoms to increase the p-type activation efficiency, and also to perform plasma annealing or heat treatment to completely remove residual Mg-H composites. It is.

The p-type activation method of the present invention for achieving the above object is a first step of growing a GaN buffer layer on a sapphire substrate at a predetermined height and temperature by an organometallic chemical vapor deposition method, and a GaN thin film doped with magnesium in the GaN buffer layer Is grown to a constant thickness at a high temperature, and the GaN thin film is grown using nitrogen gas as a main flow to activate the grown GaN thin film, and then on a support heated to a constant temperature in a vacuum vessel of 10 ^-3 Torr. And a third step of annealing the thin film to nitrogen plasma.

The p-type activation method having another feature of the present invention is an epitaxial growth process of performing a p-type thin film layer in a nitrogen gas main flow atmosphere when growing a multi-layer gallium nitride thin film by organometallic chemical vapor deposition; A photoactivation process of irradiating a substrate surface by a halogen lamp set upon growth of the thin film layer, and a process of applying a high density nitrogen plasma by an electronic circuit process to a thin film sample mounted on a high temperature substrate support after performing the process. It is characterized by that.

Preferably, the GaN buffer layer is grown at 520 ° C. with a height of about 30 nm.

Preferably, the GaN thin film is characterized by growing to a thickness of about 1.7㎛ at 1100 ℃ high temperature.

Preferably, the grown GaN thin film is characterized in that it is mounted in a vacuum chamber heated to a temperature of about 800 ℃.

Preferably, the nitrogen plasma treatment process is characterized in that for 20 minutes.

Preferably, in the vacuum vessel of 10 ⁻³ Torr or less, the hydrogen atoms in the thin film are excited by a nitrogen or argon plasma atmosphere at a temperature of 800 ° C. for 20 min.

Preferably, the plasma has a frequency of 254 GHz and the plasma power is characterized by having a 300 $.

Preferably, in order to activate the GaN thin film, a UV lamp is irradiated to the surface of the growing substrate while the thin film is grown, or a halogen lamp is used to reduce interdiffusion between interfaces of magnesium atoms.

Preferably, the magnesium doping source and the silicon or zinc doping source having a relatively high diffusion barrier are mixed and co-doped at a predetermined ratio to reduce strain energy due to atomic distortion between lattice and to have high activity of hole carrier concentration. do.

1 is a view schematically showing an electron rotating resonance plasma apparatus used in the present invention

2 is a schematic view showing a p-GaN thin film structure grown by the organometallic chemical vapor deposition method of the present invention

3 is a graph showing the intensity of an emission spectrum of a thin film surface heat-treated after p-GaN thin film growth using a hydrogen gas source as a main flow gas flowing into a reactor;

4 is a graph showing the intensity of the spectrum of a thin film surface after p-GaN thin film growth using a nitrogen gas source as the main flow gas flowing into the reactor;

5 is a graph showing the intensity of the emission spectrum of the surface of the thin film annealed plasma after p-GaN thin film growth using a nitrogen gas source as the main flow gas flowing into the reactor;

6 is a light emission intensity (A) of a thin film grown with a nitrogen gas source according to a magnesium (Mg) doping source and an annealing intensity (B) and a hydrogen gas source from a thin film grown with a nitrogen gas source. A diagram comparing the emission intensity (C) of the grown and heat treated thin films

7 shows free hole carrier concentration (A) of a thin film grown with a nitrogen gas source according to the content of magnesium doping source and annealing plasma, and a free hole carrier concentration (B) and hydrogen gas from a thin film grown with a nitrogen gas source. A diagram showing the free hole carrier concentration (C) of a thin film heat-grown into a circle

8 is a view showing the resistance (A) of a thin film grown with a nitrogen gas source according to the content of magnesium doping source and annealing the plasma, and the resistance (B) of a thin film grown with a hydrogen gas source and heat treated.

FIG. 9 is an infrared absorption diagram showing a vibration mode having a momentum of 3125 cm ⁻¹ in an Mg-H composite of p-type gallium nitride thin film, in which a gallium nitride thin film grown as a hydrogen gas source (A) and a hydrogen gas source are grown. Shows gallium nitride thin film thermally treated by heat treatment (B), gallium nitride thin film grown with nitrogen gas source (C) and gallium nitride thin film grown with nitrogen gas source and annealed by plasma (D)

Explanation of symbols on the main parts of the drawing

1: bell jar 2: nitrogen gas

3: exhaust 4: magnet

5: Substrate 6: Substrate Support

7: Microwave Generator 8: Plasma

9: sapphire substrate 10: GaN buffer layer

11: P-GaN thin film

This preferred embodiment enables a better understanding of the objects, features and advantages of the present invention.

Hereinafter, a preferred embodiment of the p-type activation method by plasma annealing of magnesium-doped gallium nitride-based thin film grown by the organometallic chemical vapor deposition method according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a view schematically showing an electron rotating resonance (ECR) plasma apparatus used in the present invention, in which electrons excited by a plasma 8 generated inside a vacuum vessel as shown in FIG. It rotates according to the magnetic field of 875 Gauss generated by 4). At this time, by applying microwave with the frequency of 2.45 GHz that electron can resonate, it causes resonance and maximizes the energy of electrons. The collision frequency is increased to obtain a high density plasma, and the nitrogen gas is supplied to form the plasma.

In addition, the substrate support 6 was manufactured to be able to heat 800 degreeC or more and to apply DC bias. Plasma shielding (sheath potential) is achieved by nitrogen ions, and the nitrogen ions are accelerated toward the substrate 5 and the ionization effect is high, thereby enabling plasma annealing at a low pressure of 10 ^-3 Torr.

FIG. 2 is a schematic view showing a p-GaN thin film structure grown by the organometallic chemical vapor deposition method of the present invention. As shown in FIG. 2, the GaN buffer layer 10 is 520 ° C. on the sapphire substrate 9 at a height of 30 nm. After growing at, the p-GaN thin film 11 doped with magnesium in the GaN buffer layer 10 is grown to a thickness of 1.7 μm at a high temperature of 1100 ° C.

Trimethylgallium (TMGa) and vice cyclopentadienyl magnesium ((C ₅ H ₅ ) ₂ Mg: Cp ₂ Mg) were used as the GaN matrix and the doping source, respectively. 60 sccm and 18 sccm are used, respectively, and 4 slm of ammonia gas and 6 slm of hydrogen gas are used in the main flow of the reactor. In addition, GaN thin film is grown by converting hydrogen gas in the main stream into nitrogen gas.

When hydrogen gas is used in the main flow for p-type activation of the p-GaN thin film thus grown, it is heated to a temperature of 800 ° C. for 5 min in a vacuum vessel of 10 ⁻³ Torr, followed by rapid heat treatment in a nitrogen gas atmosphere at atmospheric pressure. (RTP) is performed for 20 min. In addition, when nitrogen gas is used as the main flow, plasma annealing is performed in the same 10 ^-3 Torr vacuum vessel, and in the rapid heat treatment, after the crystal growth in the MOCVD reactor using RF heating, it is cooled to room temperature. Heat treatment may be carried out on a hot plate such as PBN, or rapid heat treatment may be performed using a halogen lamp or tungsten lamp. In a particularly preferred case, by rapid heat treatment using a lamp heating method, the mutual diffusion of magnesium at the p-GaN semiconductor interface can be reduced.

FIG. 3 shows light emission characteristics PL when hydrogen gas is grown using a flow rate of Cp ₂ Mg as a main flow gas using 18 sccm, and subsequent heat treatment is performed at 800 ° C. for 20 min. This luminescent property is due to the desorption of hydrogen atoms while magnesium atoms form a complex with hydrogen and are activated by thermal energy. Holes are bound around the magnesium atom at the Ga (gallium) position in the GaN crystal to form a deep level center acting as an acceptor, where the acceptor binding energy is about 0.25 eV.

The binding energy is much higher than 0.027 eV and 0.055 eV of GaAs or GaP. When the magnesium atom acts as an acceptor at the Ga position, the electron atom of the N atom at the anion lattice position is very large, This is because the coupling attempts to stabilize the electrical potential. Chemical reaction formula according to the activation energy supplied here is shown in the formula (1).

One

GaN: MgH + 0.25eV → GaN: Mg · +-H ₂ .......... (1)

2

In addition, p-typed by Zn or Cd doping is very difficult to activate because the binding energy in the GaN thin film is increased to 0.33 eV, 0.55 eV, and the hole is compensated.

On the other hand, Figure 4 shows the light emission characteristics measured in the state of the thin film grown when the main flow gas is used as nitrogen gas, and shows similar light emission characteristics as the case of subsequent heat treatment using hydrogen gas as the main flow gas. In addition, it can be seen that the GaN thin film layer is partially p-type activated because magnesium atoms separated from the organometallic of Cp ₂ Mg do not have direct contact with the hydrogen gas source.

FIG. 5 shows that the emission intensity is greatly increased due to the emission characteristics measured after plasma annealing the p-GaN thin film grown in the nitrogen atmosphere of FIG. 4. This increase is due to the fact that when nitrogen gas is used as the main flow gas source, hydrogen desorbed from an organometallic source or ammonia gas provides a low diffusion barrier due to the very high electronegativity of the nitrogen atom, and easily participates in the reaction and then desorbed by heat treatment. Because. In addition, the high dielectric constant due to the bonding of hydrogen shows that the dielectric constant rapidly decreases as the hydrogen atoms of the Mg-H complex dissociate and are activated by forming an acceptor center of a deep level.

This is very different from the case of GaAs or GaP where the energy gap is relatively small. Usually, they form only a thin level, which increases the free hole carrier concentration of the p-type thin film and, conversely, decreases the carrier concentration when the deep level is formed. On the other hand, GaN thin films with wide energy gaps can be p-typed only when deep-level acceptors are formed and p-typed can be estimated from luminescent properties, and holes in a multi-layered structure such as a double hetero structure It is very useful to check p-type activation from luminescence properties when (Hall) effect measurement is impossible.

Figure 6 is a characteristic diagram comparing the luminescence characteristics according to the flow rate change of the magnesium doping source, it can be seen that the hydrogen gas effect of the main flow gas correlated with the heat treatment effect, the optimized flow rate is 18 sccm (3.6μmol / min) It can be confirmed that. 6 (A) shows the case of annealing in a low vacuum nitrogen plasma state after growing in a main flow atmosphere of nitrogen gas, FIG. 6 (B) shows the case of measuring in a grown thin film state, and FIG. 6 (C) shows hydrogen. The same heat treatment was performed on the GaN thin film grown in the main gas flow state.

FIG. 7 is a characteristic diagram measuring the concentration of free hole carriers in each thin film manufactured according to the flow rate of magnesium doping source, and shows a maximum of 8 × 10 ¹⁸ / cm 3 when grown in a nitrogen gas stream and plasma annealed (A). In the case of the grown thin film (B), it shows a maximum of about 2 × 10 ¹⁸ / cm 3, which is much higher than the maximum of 2 × 10 ¹⁷ / cm 3 when grown in a hydrogen gas stream and heat treated (C). The characteristics of the thin film resistivity due to the activating effect are shown in FIG. 8. As shown in FIG. 8, when grown in a hydrogen gas atmosphere and subjected to heat treatment (A), while a thin film was grown in a nitrogen gas atmosphere and plasma annealed (800 mm), it exhibited a minimum value of 1 _hm (Ohm: Greek) -cm. B) has seen the lowest of the low resistance 0.08 _Ω -㎝.

The electrical and optical properties of the activation effect are dependent on the p-type formation by the decomposition of the Mg-H complex, and if possible, blocking the supply of hydrogen gas to prevent the formation of the complex or to decompose the complex formed by chemical bonding in the thin film. Electron beam treatment or heat treatment or plasma annealing the energy to desorb the hydrogen atoms, and the hydrogen atoms form a quantum particles (quantum particles) in the crystals to escape. In addition, it is possible to dissociate hydrogen atoms by irradiating ultraviolet rays during thin film growth so that energy can be decomposed during thin film growth.

9 is a characteristic diagram showing the absorption of the infrared spectrum (FTIR) of the p-GaN thin film, (A) shows the Mg-H vibration mode of the thin film grown using a hydrogen gas source, 3125 cm ^-1 (387 meV) has a vibration energy, and (B) shows that the absorption energy intensity of the Mg-H composite is decreased by subsequent heat treatment of the thin film grown from the hydrogen gas source. (C) is a vibration mode of the Mg-H composite of the thin film grown in the main flow of nitrogen gas source, showing similar characteristics to that of (B) heat treatment in the hydrogen gas source, and plasma annealing as in (D). It can be seen that the vibration mode is completely eliminated.

It is clear from the above description that according to the p-type activation method of the present invention, a p-type activation method in which a GaN thin film is grown using a nitrogen gas source as the main flow gas and then plasma annealed has a high free hole carrier concentration and a low resistance. It can reduce power consumption by providing forward hole mobility and lowering forward threshold voltage when manufacturing optoelectronic devices.

In addition, high resistance due to low concentration of carriers affects conductivity, requiring high applied voltage during ohmic contact of the p-type electrode. However, this improvement improves not only high carrier concentration but also hole mobility, thereby increasing external quantum efficiency. It is possible to increase the efficiency and to direct the optoelectronic device of high brightness.

Claims (11)

A first step of growing a GaN buffer layer on a sapphire substrate at a predetermined height and temperature by organometallic chemical vapor deposition; Growing a GaN thin film doped with magnesium into the GaN buffer layer at a high temperature at a constant thickness; In order to activate the grown GaN thin film and grown using nitrogen gas as the main flow, and grown by an organometallic chemical vapor deposition method comprising a third step of annealing with plasma in a vacuum vessel of 10 ^-3 Torr P-type activation method by plasma annealing of magnesium-doped gallium nitride-based thin film. 2. The p-type activation method of claim 1, wherein the GaN buffer layer is grown at a height of about 30 nm at 520 DEG C. The magnesium-doped gallium nitride based thin film grown by the organometallic chemical vapor deposition method. 2. The p-type activation according to claim 1, wherein the GaN thin film is grown to a thickness of about 1.7 μm at a high temperature of 1100 ° C. by plasma annealing of the magnesium-doped gallium nitride-based thin film grown by organometallic chemical vapor deposition. Way. The method according to claim 1, wherein in the vacuum vessel of 10 ⁻³ Torr or less, the substrate is mounted on a substrate support maintaining a temperature of 800 ° C. to anneal hydrogen atoms in the thin film by annealing for 20 min in a nitrogen or argon plasma atmosphere. A p-type activation method by plasma annealing of a magnesium-doped gallium nitride based thin film grown by organometallic chemical vapor deposition. The method of claim 1, wherein in order to activate the GaN thin film to the plasma annealing of the magnesium-doped gallium nitride-based thin film grown by the organometallic chemical vapor deposition method characterized in that irradiating the ultraviolet light to the surface of the substrate growing during the growth of the thin film. P-type activation method. The method according to claim 1, wherein the magnesium doping source and the silicon or zinc doping source having a relatively high diffusion barrier are mixed and co-doped at a predetermined ratio to reduce strain energy due to atomic distortion between lattice and to have high activity of hole carrier concentration. A p-type activation method by plasma annealing of a magnesium-doped gallium nitride based thin film grown by organometallic chemical vapor deposition. The method of claim 1, wherein as the organometallic source, trimethylgallium and vice cyclopentadienyl magnesium are used as the GaN matrix and the doping source, respectively, and the return gas uses hydrogen gas at 60 sccm and 18 sccm, respectively. P-type activation method by plasma annealing of magnesium-doped gallium nitride-based thin film grown by organometallic chemical vapor deposition. The organic metal chemical vapor deposition method according to claim 1, wherein the growth of the GaN thin film using a nitrogen gas as a main flow gas is performed for 20 min at 800 ° C. of a halogen lamp or a PBN hot plate to activate Mg. P-type activation method by plasma annealing of magnesium-doped gallium nitride-based thin film. Growing a multi-layer gallium nitride semiconductor thin film by using the main flow gas of the hydrogen gas source by organometallic chemical vapor deposition; When the p-GaN thin film is grown during the process, using a main flow gas of a nitrogen gas source; P- by plasma annealing of the magnesium-doped gallium nitride-based thin film grown by organometallic chemical vapor deposition, characterized in that the step of annealing the high-density nitrogen plasma by electron rotation resonance by a high temperature substrate support. Mold activation method. 10. The method according to claim 9, wherein the hydrogen gas or the hydrogen / nitrogen mixed gas is used as the main flow gas in the reactor. P by plasma annealing of magnesium-doped gallium nitride-based thin film grown by organometallic chemical vapor deposition. -Type activation method. The organic metal chemical vapor deposition method according to claim 9, wherein the multilayer thin film of gallium nitride is heat-treated in a reaction furnace to determine magnesium acceptor formation as a measure from the light emission characteristics of a deep level of photoluminescence. P-type activation method by plasma annealing of grown magnesium-doped gallium nitride based thin film.