TW201305398A - Group III nitride based multilayer stack structure, component having the structure and method for manufacturing the structure - Google Patents

Abstract

A group III nitride based multilayer stack structure is disclosed. The structure includes a group IV substrate (101), and a AlxGayIn1-x-yN based seed layer (102) and a AlxGayIn1-x-yN layer (103) on the group IV substrate (101), wherein the AlxGayIn1-x-yN based seed layer disposed on the substrate (101) wherein x > 0.2, and for the AlxGayIn1-x-yN layer (103), x < 0.2 and x+y ≤ 1.

Description

Multilayer stack structure based on group III nitride, component with the multilayer stack structure And a method of manufacturing the multilayer stacked structure

The present invention relates to a multilayer stack structure, and more particularly to a multilayer stack structure based on a Group III nitride.

Multilayer stack structures based on Group III nitrides are extremely suitable for a wide range of applications based on direct bandgap, such as light-emitting diodes and high voltage and high frequency transistors. In addition, it is extremely suitable for illuminants, photodetectors and photocells by theoretically greatly adjustable bandgap, which is based on GaN based on 6.5 eV of aluminum nitride (AlN) in the UV band. 3.4 eV of GaN) up to 0.68 eV based on indium nitride (InN) in the IR band. Most of the current photocells are based on germanium, and recently photovoltaic cells have been realized by chalcogenides and III-V semiconductors. Most of the III-V semiconductors involve multiple solar cells based on arsenide or phosphide, which are extremely efficient but relatively expensive.

Group III nitrides have great advantages in temperature stability, chemical resistance and radiation resistance compared to conventional batteries. Radiation resistance is important for space applications. The growth of Group III nitrides on a large number of heterogeneous substrates such as sapphire or tantalum carbide (SiC) has been known for several years, and growth on germanium substrates is becoming more and more important based on the advantages of scaling and price. For this purpose, a group III nitride layer is usually provided on SiC and germanium (Si), and the group III nitride layer has an aluminum-containing layer of AlGaN (SiC) or AlN (Si and SiC) type, thereby realizing most of A component layer based on a thick gallium nitride buffer material.

There are many reasons why these are not suitable for solar cells. The conversion of tantalum/aluminum nitride results in a high barrier and an insulation transition that is not suitable for vertical currents. Ager et al. [Joel W. Ager III, et al., Phys. Status Solidi C 6, S413 (2009)] indicate that the valence band and the indium concentration between p-Si and n-GaInN are >30%. The band offset between the GaInN conduction bands disappears, which causes an almost disappearing resistance at the interface. Such a conversion is advantageous not only for a large number of components, such as a vertical diode for switching or for LEDs, but also for solar cells.

The main problem in the fabrication of the GaInN buffer layer is the growth, especially on germanium substrates, where the reaction between gallium and germanium results in so-called reflow etching [siehe zBKapitel IV von A.Dadgar in III-V Compound Semiconductor:Integration With Silicon-based Microelectronics , Editoren T. Li, M. Mastro, und A. Dadgar (CRC Press, Boca Raton, FL, 2010). This remelting etch (especially as the layer separates from the gas phase during the process) results in the formation of pores in the ruthenium substrate and results in the formation of ruthenium-nitrogen-rich precipitates or growth due to precipitated ruthenium. The layers are heavily and mostly undesirably doped with antimony. The above phenomenon is exemplarily shown in Fig. 4, in which the germanium substrate (401) is grown with GaInN (402), and the portion of the hole formed in the substrate (403) by reflow etching is again filled with GaInN full. The growth of the GaInN seed layer causes the layers that are in contact there to be severely disorganized. Regardless of the reflow etching, the nucleus (Bekeimung) with such a compound on various substrates (for example, Si, germanium (Ge), diamond (C) or a mixture thereof) is not ideal in itself, and This causes the crystal to show significant rotation and dumping as shown in Figure 4 and has a negative impact on the properties of the layers and components.

In order to obtain low resistance in vertical conduction, a lower semiconductor strip offset is sought in the case where the crystal quality is as good as possible. In principle, this can be achieved by means of GaInN [Joel W. Ager III, et al. , Phys.Status Solidi C 6, S413 (2009)]. Here, the problem of directly growing a GaN layer on the germanium and remelting etching is well known and poses an unsolved problem. It is also known to use an AlN-based seed layer in order to avoid reflow etching, which is not suitable for vertical currents, although it has a high band gap energy. [siehe zBKapitel IV von A.Dadgar in III-V Compound Semiconductor: Integration with Silicon-based Microelectronics , Editoren T. Li, M. Mastro, und A. Dadgar (CRC Press, Boca Raton, FL, 2010).]

It is an object of the present invention to address the problems of reflow etching, low crystal quality, and generally high vertical resistance that occur on conventional seed layers.

These purposes will be based on Group III nitrides according to item 1 of the scope of the patent application. Multi-layer stack structure and components with a group III nitride-based multilayer stack structure according to claim 7 of the patent application, and a group III nitride-based multilayer stack structure according to claim 8 The manufacturing method is implemented. Preferred embodiments of the invention are presented in the dependent claims.

According to the present invention, there is provided a multilayer stack structure based on a Group III nitride, the multilayer stack structure comprising at least: a Group IV substrate (101), and an Al _x Ga _y on the Group IV substrate (101) In _1-xy N-based seed layer (102) and an Al _x Ga _y In _1-xy N layer (103); wherein the seed layer (102) arrangement based on Al _x Ga _y In _1-xy N On the substrate (101) and x>0.2, and x<0.2 and x+y of the Al _x Ga _y In _1-xy N layer (103) 1.

The advantage of this layer arrangement is that a better layer quality is obtained compared to a multilayer stack structure with seed layers and Al < 20%, in particular the suppression of gallium and etched etching in the literature. The reaction of ruthenium and the electrical resistance of the III-nitride/germanium interface are very low. Here, the percentage value of the group III element is always related to its component in the group III element, that is, the total concentration of the group III element is 100%.

The invention will be described below using applications in solar cells, but is not limited thereto, and in principle the invention is applicable to all applications dedicated to obtaining vertical currents. Here, the seed layer is a group III nitride layer, which has different symmetry (for example, in a two-coordinate (110), three-coordinate (001), and four-coordinate (111) symmetry with surface atoms. In the case of a sphalerite structure [A. Dadgar et al., New Journal of Physics 9, 389 (2007) und F. Reiher, et al., Journal of Crystal Growth 312, 180 (2010)] or, for example, six known as SiC In the angular crystal), the transition from the substrate to the III-nitride buffer layer is achieved with irregular grating constants. For high quality crystals, the growing layer should be adjusted as regularly as possible. Since growth is usually based on islands, these islands must be oriented as far as possible to each other so that they do not produce or produce only a small amount of new lattice defects when polymerized into a closed layer.

Here, it is desirable to have an AlInN seed layer, that is to say a gallium-free seed layer, however, in the case where the seed layer is not significantly deteriorated and the undesired remelting etching is additionally sufficiently suppressed, a small amount of the III component is Up to 20% of the gallium mixture is also tolerable.

In order to reduce the band gap energy and thus the III nitride substrate interface A better current, a gallium mixture can be advantageous. It is important to have a sufficient concentration of aluminum to minimize the effects described above. Therefore, the aluminum concentration should be at least about 20%, and ideally more than 30%. The remaining components of the compound are advantageously composed of indium which does not cause a reflow etch. Also, in the case of high crystal orientation, there is no etch back effect on the interface for the substrate (especially from tantalum or tantalum substrate to the group III nitride layer), obtained by means of AlGaInN material rich in aluminum and indium. Very small offset. This results in a layer composed of the desired concentration of GaInN.

With this additional AlInN/GaInN interface, no additional band offset is caused in the case of a suitable choice of composition, and therefore the additional layer does not have a significant negative impact on the electrical conductivity of the overall structure. On the contrary, the conductivity is enhanced by the improved crystallographic properties.

However, it may also be desirable to obtain a low band offset on the AlInN/GaInN interface depending on the structure, respectively, thereby avoiding undesired minority carrier recombination, for example, on a multi-defect AlInN layer placed next to the substrate. Therefore, in the case where holes (Loch) are minority carriers, a small barrier (Barriere) in the valence band is advantageous, and similarly, in the case where electrons are minority carriers, in the conduction band Small barriers are also advantageous for optoelectronic applications in particular.

The barrier can reflect minority carriers to a certain extent and diffuse to the space charge region, rather than recombining in the range of the germanium interface or near the germanium interface, which improves efficiency. These can also be achieved by the reverse field generated by the dopant and by the piezoelectric field generated on the different interface AlInN/GaInN.

Another embodiment of the present invention provides a multilayer stack structure in which the band gap energy of the AlGaInN seed layer is lower than the band gap energy of the layer to which it is attached.

Compared with GaInN, it is generally attempted to make the In content in AlInN higher because AlInN has a slightly higher band gap energy.

In a photovoltaic cell in which a group III nitride-based multiple battery is combined with a germanium-based battery, AlInN, which is originally used as a seed layer, can also be used as a photovoltaic cell, but must be made of a corresponding thickness of 100 nm or more, so that A multi-battery system has sufficient efficiency like a single battery.

In order to make the vertical resistance as small as possible, an n-type conductive group III nitride multilayer stack structure disposed on the surface of the p-type conductive substrate is advantageous. In multiple solar cells, conventional tunneling is not used between the cells, and it is necessary to use this transition, and this method is more useful than the delta-doped p- and n-type conductive layers used for tunnel contact. This transition is simply achieved. For example, the above arrangement can be achieved during growth by introducing one or more Group III elements prior to growing the seed layer such that the Group III element produces a p-type dopant in the surface layer of the substrate. Further, in the multilayer stacked structure, a small amount of germanium diffusion in the group III nitride species layer is also advantageous because it enhances the n-type dopant.

In accordance with another embodiment of the present invention, a multilayer stack structure is provided in which seed layer (102) is grown in an Al _x Ga _y In _1-xy N, y < 0.2 system.

One embodiment of the invention proposes to apply the multilayer stack structure in a diode or photovoltaic cell.

Another embodiment of the present invention is a component having a multilayer stack structure based on a Group III nitride, the component comprising at least Al _x Ga _y In _1-xy N on a Group IV substrate (101) Seed layer (102) and Al _x Ga _y In _1-xy N layer (103), where x < 0.2, wherein Al _x Ga _y In _1-xy N layer (102), which is Al _x Ga _y In _{The 1-xy} N based seed layer (102) is disposed on the substrate (101) and is at least x > 0.2.

According to another embodiment of the present invention, there is provided a method of fabricating a multilayer stack structure based on a Group III nitride, the method of manufacturing comprising at least the steps of: (1) providing a Group IV substrate (101); (2) a seed layer (102) based on Al _x Ga _y In _1-xy N is coated on the substrate (101) and x>0.2; (3) at least one other Al _x Ga _y In is coated on the seed layer (102) _1-xy N layer (103) and x < 0.2.

Figure 1 shows a simple battery. The substrate 101 is here or merely an ideal p-type conductive carrier or an n/p type germanium battery, preferably with a p-type conductive layer directed upwardly opposite the seed layer 102. Seed layer 102 is an AlGaInN layer in accordance with the present invention. Layer 101 may also include a substrate material in a SiGeC system or a thin layer over a carrier substrate. In order to achieve better efficiency through a more compatible band gap, especially SiGe compounds for solar cells Words are helpful.

It is desirable to seed in a system of Al _x Ga _y In _1-xy N, X>20. Further, it is desirable that the seed layer has an indium (In) concentration of between 40-50% or 0.4<1-xy<0.5, and when ternary, that is, without a gallium (Ga) mixture (y=0) In case of, it can have a corresponding 60-50% (0.5 x Aluminium concentration between 0.6), which may contain a small amount of up to 20% (y 0.2) gallium.

The layer can be produced by means of metal organic vapor phase epitaxy (MOCVD, MOVPE) or other semiconductor coating methods, such as molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE) or sputtering methods, where This process is described by means of the MOVPE method for Group III nitrides at the time. To this end, a ruthenium substrate, preferably pre-deoxidized and dehydrogenated, is placed in the MOVPE reactor and heated to about 670 ° C in a hydrogen or nitrogen carrier gas.

After the carrier gas is converted to nitrogen, the coating process is ideally carried out at a pressure of about 100 mbar, first introducing trimethylaluminum (TMAl) or alternatively trimethylindium (TMIn), and where possible An n-type dopant (e.g., ruthenium or osmium) may be introduced, for example, about 10 s of GeH ₄ or SiH ₄ is supplied to the reactor, and then ammonia is supplied. An AlInN layer was grown after about 10 minutes, which layer was about 10 nanometers (nm) thick. The dopants in the AlInN layer can also get the same result as ammonia enters the reactor. It is also feasible to coat the substrate with Si or Ge or a mixture thereof in advance. It is thus also possible to epitaxially grow the p-layer or to improve the surface and/or contact properties by growing a layer composed of Si, Ge or SiGe.

After the AlInN layer is grown, the supply of TMAl and TMIn will end, and trimethylgallium (TMGa) and trimethylindium (TMIn) with dopants (usually n-type dopants) will be introduced into In the reactor, the layer 103 and the underlying layer are thus grown. However, in order to realize the following n-AlInN/p-GaInN battery, a p-type dopant can also be introduced. In this case, the seed layer 102 should be at least 50 nanometers (nm) thick.

In order to adapt the components to each other, the supply of In is still maintained during the period of growth interruption to maintain most of the existing In enriched layer on the surface of the layer and to maintain a stable In introduction. Usually InN is not generated in this program because it has excessive air pressure, which means instability.

In order to form a solar cell on an n-type germanium, an n-type germanium substrate is embedded in a coating structure, for example, molecular beam epitaxy (MBE) or metal organic vapor phase epitaxy (MOCVD). Preferably, the ruthenium substrate is subjected to wet chemical deoxidation in advance and immersed in hydrogen by means of hydrofluoric acid; the ruthenium substrate may also be formed by heating in a reactor.

The substrate is then heated and the seed layer is grown by introduction of a Group III starting material. It is not necessary to introduce these raw materials at the same time, and it is possible to introduce, for example, aluminum, by the production process control, because it easily diffuses into the crucible, and the p-type conductive skin layer expected in the present example is produced here. However, it is also advantageous to introduce indium first in order to achieve indium concentration. In order to have a uniform AlInN concentration from the beginning, this introduction is important.

Therefore, in the process, a plurality of elements may be simultaneously introduced or introduced one by one. For example, in order to form a p-type layer, Al is first introduced, and then indium is introduced for concentration, and then an aluminum source and a common nitrogen source material are opened. This layer desirably grows to a thickness of 10 to 20 nm.

In principle, a 1 nm thick AlInN layer is sufficient, but a layer thickness of 5 nm or more is more advantageous. This layer is preferably closed so that the GaInN layer that is in contact therewith does not come into contact with the substrate, as may occur when forming a recess or island growth in the seed layer. This as close coverage as possible of the substrate essentially depends on the layer thickness that is intended to be achieved.

This layer is desirably n-doped, which is usually very well achieved by means of ruthenium or osmium. This results in a characteristic of the bandgap energy E obtained by the multi-layer stack structure at the coordinate x, which is schematically shown in Fig. 2, in which case the coordinate x extends from the substrate towards the group III nitride layer, which The curved features ensure low resistance on the surface of the Group IV/III nitride. Here, E _C represents a conduction band, E _F represents a Fermi level, and E _V represents a valence band in the group IV substrate 201 and a valence band of the seed layer 202 adjacent thereto.

The joined GalnN layers are then grown at nearly the same temperature. In this step, there is the advantage that AlInN has a higher In import than GaInN and its band gap energy can be compared with GaInN based on the higher In content in AlInN.

When implementing a vertical diode, for example, for a power component, in a favorable The AlGaInN seed layer 102 is used in the embodiment, and its band gap energy is lower than the layer 103 that is in contact therewith. This leaves no additional energy barriers to interfering carrier transport in the buffer structure.

Here, a gradual transition from AlInN to GaInN is also expedient, which achieves a gradual conversion of the conduction band and valence band energy and thereby minimizes the series resistance. The example shown in Figure 3 exemplarily demonstrates this transition, representing the bandgap energy E on the coordinate x, in which case the coordinate x extends from the substrate to the Ill-nitride layer. The AlInN layer 302 is grown starting from the ruthenium substrate 301, and the layer is gradated into GaInN 304 via AlInN 303. Here, the content of In is decreased, and the band gap energy is increased as a whole.

The slope can also be increased by slightly increasing the temperature during growth or reducing the introduction of In.

Increasing the content of Ga can increase the grating constant of the material, and thus can also advantageously produce a slight compressive stress that prevents crack formation during thick layer growth. After this buffering, the material chosen for the part is followed: therefore, in order to achieve a high-voltage switch for vertical contact with high-quality GaN n/p-type diodes, it may be meaningful to slope to GaN, but also This structure can be used to realize a high current switch based on GaInN.

4 shows a cross section of a layer structure of an InGaN layer 402 directly grown on a crucible 401, as shown in a transmission electron microscope. Wherein the holes 403 in the ruthenium substrate range are clearly visible, and the holes can be opened by meltback etching. The use of the method according to the invention significantly reduces or eliminates the number of holes, thereby improving the layer quality.

The components according to the invention may also differ from the examples described herein and may be fabricated by all methods for semiconductor separation. Thus, for several components, the transition of n-type germanium or n-type Ge-/AlGaInN is also of particular interest or can achieve low series resistance at the bandgap energy of a suitable group III nitride.

In the manufacture of these layers, although epitaxial growth is generally advantageous for the characteristics of the components, it is basically not prevalent on epitaxial growth.

In addition, these layers may also contain other V group elements of a small concentration. Therefore, starting from the AlInAs layer which is converted into AlInN by nitridation, growth such as AlInN is also a meaningful way to obtain the component according to the invention.

100‧‧‧Multilayer stacking structure

101‧‧‧Substrate

102‧‧‧ layers

103‧‧‧AlGaInN layer

201‧‧‧Substrate

202‧‧‧ layers

301‧‧‧矽 substrate

302‧‧‧AlInN layer

303‧‧‧AlInN

304‧‧‧GaInN

401‧‧‧矽

402‧‧‧InGaN layer

403‧‧‧ hole

Embodiments of the present invention are exemplarily shown by the following views and are described in detail.

As an application example, the application of a multilayer stack structure in a diode is described, especially in photovoltaic cells. Wherein: FIG. 1 shows a schematic diagram of a layer structure of a multilayered stacked structure based on a Group III nitride; FIG. 2 shows a schematic curve characteristic of a band gap energy between a Group IV substrate and a seed layer; 3 shows a schematic curve characteristic of the band gap energy between the group IV substrate and the seed layer with the component gradient, and FIG. 4 shows a cross section of the layer structure of the InGaN layer in the transmission electron microscope.

100‧‧‧Multilayer stacking structure

101‧‧‧Substrate

102‧‧‧ layers

103‧‧‧AlGaInN layer

Claims (8)

A multilayer stack structure (100) based on a group III nitride, comprising at least: a group IV substrate (101), and an Al _x Ga _y In _1-xy N on the group IV substrate (101) a seed layer (102) and an Al _x Ga _y In _1-xy N layer (103); wherein the seed layer (102) based on Al _x Ga _y In _1-xy N is disposed on the substrate ( 101) and x>0.2, and x<0.2 and x+y of the Al _x Ga _y In _1-xy N layer (103) 1. The multilayer stacked structure according to claim 1, wherein the group III nitride-based multilayer stacked structure is disposed on a surface of the p-type conductive substrate. The multilayer stack structure according to claim 1 or 2, wherein the seed layer (102) based on Al _x Ga _y In _1-xy N has band gap energy, and the band gap energy is lower than the Band gap energy of Al _x Ga _y In _1-xy N layer (103). Seed layer (102) in accordance with the scope of the patent application for multi-layer structure according to any one of claims 1 to 3, wherein in the _{Al x Ga y In 1-xy} N based on _{Al x Ga y In 1-xy} N And grow in a structure with y < 0.2. The multilayer stacked structure according to any one of claims 1 to 4, wherein the multilayer stacked structure is used in a diode. The multilayer stacked structure according to any one of claims 1 to 5, wherein the multilayer stacked structure is used in a photovoltaic cell. A component having a multilayered stacked structure (100) based on a Group III nitride, comprising at least: a Group IV substrate (101), and an Al _x Ga _y In on the Group IV substrate (101) _{a 1-xy} N-based seed layer (102) and an Al _x Ga _y In _1-xy N layer (103); wherein the seed layer (102) based on Al _x Ga _y In _1-xy N is disposed On the substrate (101) and x>0.2, and the Al _x Ga _y In _1-xy N layer (103) has x<0.2 and x+y 1. A method for fabricating a multi-layer stack structure (100) based on a group III nitride, comprising at least the steps of: providing a group IV substrate (101); fabricating a deoxidized group IV substrate surface; and using the substrate (101) a seed layer (102) based on Al _x Ga _y In _1-xy N, wherein x >0.2; and coating at least one other Al _x Ga _y In _1-xy N layer on the layer (102) (103), where x < 0.2.