KR100961107B1 - Nitride semiconductor device having double hetero-junction structure active layer - Google Patents

Abstract

The nitride semiconductor device includes a first conductive type and a second conductive type nitride semiconductor layer and an active layer having a DH structure disposed between the first and second conductive type nitride semiconductor layers and formed of a single quantum well structure. The active layer of the quantum well structure has at least one polarization alleviation layer made of a nitride single crystal having an energy gap larger than that of the quantum well structure.

Piezo effect, light emitting diode, nitride, single quantum well

Description

Nitride semiconductor devices having a heterojunction (DH) structure active layer {NITRIDE SEMICONDUCTOR DEVICE HAVING DOUBLE HETERO-JUNCTION STRUCTURE ACTIVE LAYER}

The present invention relates to a nitride semiconductor device, and more particularly to a nitride semiconductor device having an active layer of the DH structure of a single quantum well structure (SQW).

In general, nitride semiconductors are widely used in green or blue light emitting diodes (LEDs) or laser diodes (LDs), which are provided as light sources in full color displays, image scanners, various signal systems, and optical communication devices. Such a nitride semiconductor device can be provided as a light emitting device having an active layer emitting a variety of light, including blue and green using the recombination principle of electrons and holes.

After such a nitride light emitting device (LED) has been developed, many technical developments have been made, and the range of its use has been expanded, and as a light source for general lighting and electric field, many studies have been conducted. In particular, in the past, nitride light emitting devices have been mainly used as components applied to mobile products of low current / low power, but recently, their application ranges are gradually expanded to high current / high power fields. Accordingly, it is urgent to develop an LED structure having high efficiency at high current.

The light efficiency of nitride semiconductor devices such as LEDs is basically determined by the probability of recombination of electrons and holes in the active layer, that is, internal quantum efficiency.

The active layer of the nitride semiconductor device includes a single quantum well (SQW) structure having a single quantum well layer (hereinafter, also referred to as a 'DH structure active layer') and a plurality of quantum well layers smaller than about 100 Hz. There is a quantum well (MQW) structure.

In general, the active layer of the multi-quantum well structure is actively used because of its superior light efficiency and high luminous output compared to a single quantum well structure.

As shown in the graph of FIG. 1A, according to the wave function (dotted line: electron, solid line: hole), the distribution decreases as the distance from the n-type and p-type nitride semiconductor layers increases, depending on the mobility difference between electrons and holes. do. As a result, as shown in FIG. 1B, the effective recombination probability has a problem of concentrating on the quantum well layer located in the region (II) close to the p-type nitride semiconductor layer.

As such, in the active layer of the multi-quantum well structure, carrier injection may be reduced in a specific local region, thereby reducing the effective active region in the entire active layer, thereby lowering the luminous efficiency.

Therefore, in order to obtain a high-efficiency light emitting device at high power, even if the number of carriers is increased by using a thick single quantum well (SQW) structure without a quantum barrier layer (QB), it is spread throughout the single quantum well space as a whole. A single quantum well structure, ie, an active layer of DH (Double Hetero) structure, which allows the recombination rate to be maintained without decreasing (see FIG. 2A) will be preferred.

However, when a thick single quantum well layer is actually used in a nitride semiconductor device having an InGaN / GaN active layer, as shown in FIG. 2B, a very strong piezo effect occurs, resulting in a large reduction in light efficiency and a short wavelength. As a result, there is no room for increasing the growth temperature of the active layer.

Thus, in theory, the active layer of the single quantum well structure is beneficial as a method of improving the luminous efficiency by increasing the overall recombination efficiency, but suffers from the chronic problems of light efficiency and short wavelength due to the piezoelectric effect.

The present invention has been made to solve the above problems of the prior art, and an object thereof is to provide a nitride semiconductor device capable of ensuring high efficiency at high current by mitigating the problem of piezoelectric effect.

In order to solve the above technical problem, the present invention,

A first conductive type and a second conductive type nitride semiconductor layer and an active layer having a DH structure formed between the first and second conductive type nitride semiconductor layers and formed of a single quantum well structure, The active layer provides a nitride semiconductor device having at least one polarization mitigating layer made of a nitride single crystal having an energy gap larger than that of the quantum well structure.

In a particular example, the thickness of the active layer may be 100 to 250 mm 3.

The thickness of the polarization alleviating layer is preferably 10 kPa or less so as not to act as a quantum barrier by ensuring tunneling of the carrier.

Preferably, the polarization alleviating layer is plural, and the plurality of polarization alleviating layers may be arranged at regular intervals. The preferred polarization alleviating layer spacing may be 10-40 mm.

According to the present invention, the polarization problem due to the piezoelectric effect can be solved by introducing at least one polarization mitigating layer into the thick quantum well layer while employing an active layer having a single quantum well structure that can prevent the local carrier injection efficiency from dropping. have. Therefore, the output can be greatly improved at high current density, and thus it can be very advantageously applied to the high output nitride semiconductor element. In addition, the stability of the wavelength can be achieved by suppressing the blue transition in the green wavelength light emitting device, which is a problem of the thick single quantum well structure.

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

3 is a cross-sectional view showing a nitride semiconductor device having a single quantum well structure according to an embodiment of the present invention.

As shown in FIG. 3, the nitride semiconductor element 10 includes a substrate 11, an n-type nitride semiconductor layer 13, an active layer 15, and a p-type nitride semiconductor layer 17. In the n-type electrode, an n-type electrode 19a may be formed on an upper surface of the n-type nitride semiconductor layer 13 exposed by mesa etching. In addition, a transparent electrode layer 18 and a p-type electrode 19b may be sequentially formed on the upper surface of the p-type nitride semiconductor layer 17.

In the present embodiment, the structure of the horizontal nitride semiconductor light emitting device in which both electrodes 19a and 19b are disposed on the same surface is illustrated. However, the present invention is not limited thereto, and it can be easily applied to a nitride semiconductor light emitting device having a vertical structure. Will understand.

As shown in FIG. 3, the active layer 15 is an active layer having a double hetero (DH) structure having a single quantum well structure. In addition, the active layer 15 has a polarization alleviating layer 15b for alleviating the piezoelectric effect due to the thickness of the large single quantum well structure.

The polarization alleviating layer 15b may be formed of a nitride semiconductor layer having an energy band gap higher than that of the quantum well structure 15a. For example, when the quantum well structure is In _{x 1} Ga _{1-x 1} N, the quantum well structure may be formed of In _{x 2} Ga _{1-x 2} N (X 1> X 2) or GaN having a relatively small In component.

In addition, the polarization alleviating layer 15b is provided in a very thin film form unlike a conventional quantum well layer (for example, about 30 mW). More specifically, the polarization mitigating layer 15b employed in the present invention has a very thin thickness in which electrons and holes injected into the active layer 15 can be tunneled without being felt as a quantum barrier.

For this action, the thickness ta of the polarization alleviating layer 15b is preferably 10 kPa or less. In addition, the thickness ta of the polarization alleviating layer 15b is preferably 3 kPa or more in order to obtain a sufficient polarization alleviating action.

In this embodiment, it is illustrated by the form which has two polarization relaxation layers 15b. In terms of structure, the quantum well structure 15a is divided into three regions by the two polarization alleviating layers 15b, but as described above, the polarization alleviating layer 15b has a very thin thickness. Since it does not function as a quantum barrier, it can be understood as the same structure as a single quantum well structure, and in the thickness range of the polarization alleviating layer 15b, the carrier injected into the active layer 15 is different from that of the single quantum well structure. You can do the same.

Although illustrated in the form of having a plurality of polarization alleviating layers in this embodiment, it will be apparent to those skilled in the art that similar effects can be expected even if one polarization alleviating layer is employed depending on the thickness of a single quantum well structure.

The thickness t of the active layer 15 of the DH structure employed in the present invention may be 100 to 250 mm 3. If it is less than 100 μs, it is difficult to sufficiently obtain the advantage of maintaining a high recombination efficiency in the entire area as a single quantum well structure, and if it is more than 250 μs, the polarization relaxation problem becomes too large.

As in the present embodiment, when a plurality of polarization alleviating layers 15b are employed, it is preferable that the plurality of polarization alleviating layers 15b be arranged at a constant interval d. In order to maximize the polarization alleviating effect, it is preferable to design the interval d of the polarization alleviating layer 15b to 10 to 40 kV.

FIG. 4 is a band diagram showing an active layer region of the nitride semiconductor device shown in FIG. That is, the region shown in FIG. 4 can be understood as the active layer 15 of FIG. 3 and the surrounding portion thereof. Here, the vertical axis refers to the absolute size (eV) of the energy band gap, and the horizontal axis refers to the distance in the vertical direction from the n-type nitride semiconductor layer to the p-type nitride semiconductor layer.

In this diagram, more specifically, the n-type and p-type nitride semiconductor layers 13 and 17 are illustrated as n-type and p-type GaN, respectively, and the n-type nitride semiconductor layer 13 and the p-type nitride semiconductor layer 17 The active layer 15 located in between is illustrated as a single quantum well structure of InGaN.

As shown in FIG. 4, the quantum well structure of the active layer 15 is divided into three regions 15a by polarization alleviating layers 15b arranged at regular intervals. The polarization mitigating layer 15b has an energy band gap higher than that of the quantum well structure, and it can be understood as illustrated here as GaN.

As described above, the polarization alleviating layer 15b has a thin thickness so that the carrier is tunnelable. That is, the polarization mitigating layer 15b does not act as a quantum barrier due to a very thin thickness ta, even if it is made of a semiconductor material having the same composition as a conventional quantum barrier layer.

Therefore, even if the thickness t of the single quantum well structure active layer 15 is considerably large, the actual length causing the polarization action is limited to the interval between the polarization mitigating layers, so that the effect of the overall piezoelectric effect can be greatly reduced. .

As such, the piezoelectric effect can be reduced by appropriately employing the polarization alleviating layer in a single quantum well structure. As a result, the green wavelength that can be caused by the light emitting device used at high power has a blue-shift phenomenon. By suppressing this, the effect of achieving stability of the wavelength can be expected.

The above-described embodiments and the accompanying drawings are merely illustrative of preferred embodiments, and the present invention is intended to be limited by the appended claims. In addition, it will be apparent to those skilled in the art that the present invention may be substituted, modified, and changed in various forms without departing from the technical spirit of the present invention described in the claims.

1A and 1B are graphs showing a carrier wave function and an effective active region in an active layer of a conventional multi-quantum well structure, respectively.

2A and 2B are schematic diagrams schematically showing a theoretical band diagram and an actual band diagram according to piezoelectric polarization of an active layer of a conventional single quantum well structure, respectively.

3 is a cross-sectional view showing a nitride semiconductor device having a single quantum well structure according to an embodiment of the present invention.

FIG. 4 is a band diagram showing an active layer region of the nitride semiconductor device shown in FIG.

Claims (5)

First and second conductive nitride semiconductor layers; And Located between the first and second conductivity type nitride semiconductor layer, and comprises an active layer of a DH structure consisting of a single quantum well, The active layer has at least one polarization mitigating layer made of a nitride single crystal having an energy gap larger than that of the single quantum well, The at least one polarization alleviating layer is nitride semiconductor device, characterized in that arranged so that the single quantum well is divided into at least two regions. The method of claim 1, The thickness of the said active layer is a nitride semiconductor element characterized by the above-mentioned. The method of claim 1, The thickness of the polarization alleviating layer is nitride semiconductor element, characterized in that less than 10 GPa. The method of claim 1, And a plurality of polarization alleviating layers, and the plurality of polarization alleviating layers are arranged at regular intervals. The method of claim 4, wherein The nitride semiconductor device, characterized in that the arrangement interval of the polarization alleviating layer is 20 to 50 kPa.

Images