JP2006245165A - Semiconductor light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element for improved element's illumination efficiency. <P>SOLUTION: An n-side intermediate layer 12 and a p-side intermediate layer 14 of Al<SB>a</SB>In<SB>b</SB>Ga<SB>1-a-b</SB>N (0<a≤0.2, 0<b≤0.2) are provided on both sides of an active layer. By appropriately adjusting Al composition and In composition of the n-side intermediate layer 12 and p-side intermediate layer 14, a band gap is provided, which is larger than the energy corresponding to the emission wavelength of the active layer 13, and the effect of polarization field is relaxed at the interface with an adjoining layer. The n-side intermediate layer 12 and p-side intermediate layer 14 may have a structure, consisting of a single composition and may have a gradient structure, in which Al composition and In composition are changed in the thickness direction. They may comprise a multiplex structure, where a layer of Al<SB>w</SB>In<SB>x</SB>Ga<SB>1-w-x</SB>N (0<w<1, 0<x<1) and a layer of Al<SB>y</SB>In<SB>z</SB>Ga<SB>1-y-z</SB>N (0<y<w, x<z<1) are laminated alternately. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor light emitting device such as a light emitting diode (LED) or a semiconductor laser.

  In recent years, semiconductor light-emitting elements such as LEDs that emit light from the visible region to the ultraviolet region have been realized with nitride-based III-V group compound semiconductors, and are applied to image display devices, illumination devices, and the like.

  Here, the basic structure and operation of a general LED will be briefly described. In the LED, a pair of carrier confinement layers are formed on a substrate, and an active layer serving as a light emitting region is provided between the pair of carrier confinement layers. In the LED having such a structure, when a voltage is applied to the pair of carrier confinement layers, electrons are injected from one carrier confinement layer and holes are injected from the other carrier confinement layer into the active layer. The electrons and holes injected into the active layer are recombined to generate photons (emit light).

  By the way, the pair of carrier confinement layers is for injecting carriers into the active layer efficiently and confining the carriers in the active layer efficiently. The carrier confinement layer is made of AlGaN (aluminum / gallium / nitrogen) or For example, Patent Document 1 discloses a technique for improving carrier confinement by using InGaN (indium / gallium / nitrogen).

JP 2003-152219 A

  However, when the carrier confinement layer is made of AlGaN, carriers can be confined efficiently, but an energy barrier for injecting carriers is formed at the interface with the adjacent layer. On the other hand, when the carrier confinement layer is made of InGaN, InGaN deteriorates due to heat applied during the manufacturing process. Therefore, there is a possibility that the light emission efficiency of the element is lowered.

  The present invention has been made in view of such problems, and an object thereof is to provide a semiconductor light emitting device capable of improving the light emission efficiency of the device.

  In the semiconductor light emitting device of the present invention, a group III-V compound semiconductor layer containing at least In and Al is disposed on both sides of the active layer.

  In the semiconductor light emitting device of the present invention, the group III-V compound semiconductor layer is disposed on both sides of the active layer, and includes at least In and Al. As a result, the Al composition and the In composition of the III-V compound semiconductor layer are appropriately adjusted so that the band gap is larger than the energy corresponding to the emission wavelength of the active layer, and the interface with the adjacent layer is set. It becomes possible to reduce the influence of the polarization field at. Here, the III-V compound semiconductor layer has a function of injecting carriers into the active layer and confining carriers in the active layer.

  According to the semiconductor light emitting device of the present invention, at least In and Al are included, and the III-V group compound semiconductor layers disposed on both sides of the active layer are provided. The Al composition and the In composition are appropriately adjusted so that the band gap is larger than the energy corresponding to the emission wavelength of the active layer, and the influence of the polarization field at the interface with the adjacent layer is reduced. It becomes possible. Thereby, carriers can be efficiently confined in the active layer, and carriers can be efficiently injected into the active layer. As a result, the internal quantum efficiency can be improved as the current density increases.

  In addition, the action of Al can prevent the III-V compound semiconductor layer itself from being deteriorated by heat applied during the manufacturing process, can improve the light transmittance, and can improve the luminous efficiency of the device. Will improve.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1A shows a cross-sectional structure of a light-emitting diode (LED) 1 according to an embodiment of the present invention. The light emitting diode 1 includes an n-type layer 11, an n-side intermediate layer 12 (III-V group compound semiconductor layer), an active layer 13, and a p-side intermediate layer 14 (III-V group compound semiconductor layer) on one surface side of a substrate 10. ), A cap layer 15 and a p-type layer 16 are stacked in this order. A p-side electrode 17 and an n-side electrode 18 are formed on part of the surface of the p-type layer 16 and the n-type layer 11, respectively. The light emitting diode 1 is a top emission type light emitting element configured to emit light emitted from the active layer 13 from the surface of the p type layer 16.

  The n-type layer 11, the n-side intermediate layer 12, the active layer 13, the p-side intermediate layer 14, the cap layer 15, and the p-type layer 16 are each composed of a nitride III-V group compound semiconductor. Note that the nitride-based III-V group compound semiconductor is a compound containing a group 3B element in the short-period periodic table, such as aluminum (Al), gallium (Ga), indium (In), and nitrogen (N). It refers to semiconductors.

The n-side intermediate layer 12 and the p-side intermediate layer 14 are composed of undoped (undoped impurities) Al _a In _b Ga _1-ab N (0 <a <1, 0 <b <1). The n-side intermediate layer 12 and the p-side intermediate layer 14 have a band gap that is larger than the energy corresponding to the emission wavelength of the active layer 13 and smaller than that of the n-type layer 11 and the p-type layer 16.

  The values of the Al composition and the In composition of the n-side intermediate layer 12 and the p-side intermediate layer 14 are determined in consideration of the carrier confinement property and the injection property with respect to the active layer 13. Specifically, the Al composition value a is preferably greater than 0% and 20% or less, more preferably 0.001% or more and 6% or less, and the In composition value b is less than 0%. It is desirably 20% or less, and more desirably 0.001% or more and 5% or less. The thickness is preferably 2 nm or more and 3000 nm or less, and more preferably 10 nm or more and 250 nm or less. However, the n-side intermediate layer 12 and the p-side intermediate layer 14 do not have to have the same composition and thickness, and may have different compositions and thicknesses.

The active layer 13 has a multiple quantum well structure in which, for example, quantum well layers and barrier layers are alternately stacked. For example, the undoped In _c Ga _1-c N (quantum well layer) / undoped In _d Ga _{1− d} N (barrier layer) (0 <c <1, 0 <d <c) is set as a set, and a plurality of layers are stacked.

  The In composition values c and d of the active layer 13 are determined in consideration of the emission wavelength, emission wavelength width, light density, and the like. Specifically, the In composition value c of the quantum well layer is preferably greater than 0% and 30% or less, and the In composition value d of the barrier layer is greater than 0% and 10% or less. desirable. The thickness of the quantum well layer is preferably 1 nm or more and 4 nm or less, and the thickness of the barrier layer is preferably 4 nm or more and 50 nm or less. Further, the thickness of the entire active layer 13 is preferably 6 nm or more and 1000 nm or less.

The cap layer 15 is made of, for example, p-type Al _e Ga _1-e N (0 <e <1) with a thickness of 30 nm. It is desirable that the thickness be such a thickness that carriers cannot pass through due to the tunnel effect, and that the value e of the Al composition is higher. By adopting such a configuration, it is possible to suppress the propagation of heat to the active layer 13 and to prevent carrier overflow in the active layer 13.

The substrate 10 is made of, for example, a 430 μm-thick gallium nitride (GaN) substrate or sapphire (Al ₂ O ₃ ) substrate. The n-type layer 11 is made of n-type GaN having a thickness of 4 μm, for example, while the p-type layer 16 is made of nmp-type GaN having a thickness of 100, for example. Further, the n-type layer 11 or the p-type layer 16 mainly has a function as an n-type (p-type) contact layer for realizing a low-resistance n-type (p-type) ohmic contact. The n-type layer 11 may further have a function as a buffer layer for improving crystallinity. The p-side electrode 17 is, for example, a laminate of silver (Ag) and palladium (Pd), or a titanium (Ti) layer, a platinum (Pt) layer, and a gold (Au) layer in order from the p-type layer 16 side. The stacked layers are electrically connected to the p-type layer 16. The n-side electrode 18 has a structure in which, for example, an alloy layer of gold (Au) and germanium (Ge), a nickel (Ni) layer, and a gold (Au) layer are sequentially stacked from the substrate 10 side. And is electrically connected to the substrate 10.

  The p-type impurity contained in the cap layer 15 and the p-type layer 16 is, for example, Se, and the n-type impurity contained in the n-type layer 11 is, for example, Zn.

  The light emitting diode 1 having such a configuration can be manufactured, for example, as follows.

In order to manufacture the light emitting diode 1 of the present embodiment, a nitride III-V compound semiconductor on the substrate 10 is formed by, for example, MOCVD (Metal Organic Chemical Vapor Deposition) method. To do. At this time, for example, trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMIn), or ammonia (NH ₃ ) is used as a raw material for the nitride-based III-V group compound semiconductor. For example, hydrogen selenide (H ₂ Se) is used, and dimethyl zinc (DMZn), for example, is used as the acceptor impurity raw material.

  Specifically, first, the n-type layer 11, the n-side intermediate layer 12, the active layer 13, the p-side intermediate layer 14, the cap layer 15, and the p-type layer 16 are laminated on one surface side of the substrate 10 in this order.

  However, when the n-side intermediate layer 12, the active layer 13, and the p-side intermediate layer 14 are stacked, the supply of impurities is stopped. Thus, ideally, these layers can be undoped, but in reality, these layers have a slight impurity concentration due to diffusion of impurities from adjacent layers.

  Next, for example, a mask layer (not shown) is formed on the p-type layer 16, and the p-type layer 16, the cap layer 15, and the p-side intermediate layer are formed by reactive ion etching (RIE). 14. The active layer 13 and the n-side intermediate layer 12 are selectively removed. Thereby, a part of the n-type layer 11 is exposed and a mesa-shaped stacked structure is formed on the n-type layer 11.

  Subsequently, the p-side electrode 17 is formed on a part of the surface of the p-type layer 16, and the n-side electrode 18 is formed on a part of the surface of the exposed part of the n-type layer 11. In this way, the light emitting diode 1 is manufactured.

  Next, the operation and effect of the light emitting diode 1 will be described.

  In the light emitting diode 1, when a voltage is applied to the n-side intermediate layer 12 and the p-side intermediate layer 14, electrons are injected from one n-side intermediate layer 12 into the active layer 13 from the other p-side intermediate layer 14. The Then, electrons and holes injected into the active layer 13 are recombined to generate photons, and emitted light is emitted from the surface of the p-type layer 16 to the outside.

  By the way, as described above, the Al composition and the In composition of the n-side intermediate layer 12 and the p-side intermediate layer 14 are determined in consideration of carrier confinement properties and injection properties with respect to the active layer 13. Qualitatively, carrier confinement improves as the value of Al composition increases, and carrier injection improves as the value of In composition increases. When considering the carrier injection property to the active layer 13, the influence of the polarization field at the interface with the adjacent layer is also taken into consideration. In this way, by appropriately adjusting the Al composition and the In composition of the n-side intermediate layer 12 and the p-side intermediate layer 14, for example, a band structure as shown in FIG. 1B can be formed. . FIG. 1B conceptually shows the band structure of the light emitting diode 1.

  As shown in FIG. 1B, the n-side intermediate layer 12 and the p-side intermediate layer 14 are larger than the energy gap of the active layer 13, and the n-side intermediate layer 12 (such as the n-type layer 11 or the p-type layer 16) ( It is smaller than the energy gap of the layer disposed between the p-side intermediate layer 14) and the n-side electrode 18 (p-side electrode 17). Further, the n-side intermediate layer 12 and the p-side intermediate layer 14 are appropriately adjusted in Al composition and In composition so that the bending of the band structure due to the influence of the polarization field does not occur at the interface with the adjacent layer. , Does not have an energy barrier when injecting carriers (mainly holes).

  As described above, according to the light-emitting diode 1 of the present embodiment, the n-side intermediate layer 12 and the p-side intermediate layer 14 made of AlInGaN are provided on both sides of the active layer 13. In addition, the Al composition and the In composition of the p-side intermediate layer 14 are appropriately adjusted so that the band gap is larger than the energy corresponding to the emission wavelength of the active layer 13, and the polarization field at the interface with the active layer 13 It is possible to mitigate the effects of As a result, carriers can be efficiently injected into the active layer 13 and carriers can be efficiently confined in the active layer 13. As a result, the internal quantum efficiency can be improved as the current density increases.

  In addition, the action of Al can prevent the n-side intermediate layer 12 and the p-side intermediate layer 14 from being deteriorated by heat applied during the manufacturing process, and can improve the light transmittance. The luminous efficiency is improved.

  The present invention has been described with reference to the embodiment. However, the present invention is not limited to the above embodiment, and various modifications can be made.

  For example, in the above embodiment, the n-side intermediate layer 12 and the p-side intermediate layer 14 are configured to be in contact with the active layer 13, but may be configured to be in contact with the active layer 13 through some layer. Good.

  In the above embodiment, the n-side electrode 18 is connected to a part of the surface of the n-type layer 11. However, when the substrate 10 is conductive, a part of the lower surface of the substrate 10 is provided. You may make it connect to.

  In the above embodiment, the active layer 13 has a multiple quantum well structure. However, the active layer 13 may have a single quantum well structure or a bulk that does not have such a quantum well structure. Also good. However, when the active layer 13 has a single quantum well structure, the In composition value c of the quantum well layer is preferably greater than 0% and 30% or less, and the In composition value d of the barrier layer is It is desirable that it is greater than 0% and 30% or less. The thickness of the quantum well layer is preferably 1 nm or more and 4 nm or less, and the thickness of the barrier layer is preferably 4 nm or more and 50 nm or less. When the active layer 13 is bulk, the In composition value of the active layer 13 is desirably greater than 0% and not greater than 20%, and the thickness of the active layer 13 is not less than 5 nm and not greater than 104 nm. Is desirable.

  Further, in the above embodiment, the n-side intermediate layer 12 and the p-side intermediate layer 14 have a single Al composition and In composition. However, for example, as shown in FIG. You may have the inclination structure which changed the composition and In composition. Such an inclined structure can be realized by adjusting the supply amounts of trimethylaluminum (TMA) and trimethylindium (TMIn) when the n-side intermediate layer 12 and the p-side intermediate layer 14 are manufactured. .

  As a result, the n-side intermediate layer 12 and the p-side intermediate layer 14 have such a tilted structure, so that the characteristics of AlGaN are utilized in the region near the substrate 10 and the characteristics of InGaN in the region near the active layer 13. It can be used. Specifically, lattice matching between the substrate 10 and the active layer 13 can be achieved. As a result, lattice defects such as misfit dislocations can be reduced.

Further, the n-side intermediate layer 12 and the p-side intermediate layer 14 are, for example, a layer made of Al _w In _x Ga _{1 -wx} N (0 <w <1, 0 <x <1) as shown in FIG. , Al _y In _z Ga _1-yz N (0 <y <w, x <z <1) and a multilayer structure in which layers are alternately stacked may be provided. Thereby, similarly to the above, lattice matching can be performed between the substrate 10 and the active layer 13, so that lattice defects such as misfit dislocations can be reduced.

  Further, the present invention is not only applied to the light emitting diode 1 as in the present embodiment, but can also be applied to a semiconductor light emitting element such as a semiconductor laser.

It is a figure showing the cross-sectional structure and band structure of the light emitting diode which concern on one embodiment of this invention. It is a conceptual diagram of In composition for demonstrating the case where the composition of the intermediate | middle layer of the light emitting diode shown in FIG. 1 is made into a gradient structure. It is a band structure diagram for demonstrating the case where the composition of the intermediate | middle layer of the light emitting diode shown in FIG. 1 is made into a laminated structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light emitting diode, 10 ... Board | substrate, 11 ... N-type layer, 12 ... N side intermediate layer, 13 ... Active layer, 14 ... P side intermediate layer, 15 ... Cap layer, 16 ... P type layer, 17 ... P side electrode 18, n-side electrode

Claims (6)

An active layer;
A semiconductor light emitting device comprising: a group III-V compound semiconductor layer containing at least In and Al and disposed on both sides of the active layer. The active layer has a multiple quantum well structure formed by alternately stacking quantum well layers and barrier layers,
The quantum well layer has an In composition of 5% to 30% and a thickness of 0.5 nm to 6 nm.
The semiconductor light emitting element according to claim 1, wherein the III-V compound semiconductor layer has an In composition lower than that of the quantum well layer and has a thickness of 2 nm to 500 nm. The III-V group compound semiconductor layer is made of Al _a In _b Ga _1-ab N (0 <a ≦ 0.2, 0 <b ≦ 0.2). The semiconductor light emitting element as described. The semiconductor light emitting element according to claim 1, wherein the III-V compound semiconductor layers are composed of different compositions. The semiconductor light emitting element according to claim 1, wherein the III-V compound semiconductor layer has an inclined structure in which an Al composition and an In composition are changed in a thickness direction. The III-V group compound semiconductor layer includes Al _w In _x Ga _{1 -wx} N (0 <w <1, 0 <x <1), Al _y In _z Ga _1-yz N (0 <y The semiconductor light-emitting device according to claim 1, wherein the semiconductor light-emitting device has a multiple structure in which layers made of <w, x <z <1) are alternately stacked.

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