KR100979701B1 - Light Emitting Diodes with Modulated Doping Layer - Google Patents

Abstract

A light emitting diode having a modulation doped layer is disclosed. The light emitting diode is interposed between an n-type contact layer, a p-type contact layer formed on the n-type contact layer, the n-type contact layer and the p-type contact layer, and an active region of a multi-quantum well structure including an InGaN layer. And a doping layer interposed between the n-type contact layer and the active region. Meanwhile, the modulation doped layer has a structure in which an n-type impurity doped InGaN layer and an undoped InGaN layer are alternately stacked, and the n-type impurity doped InGaN layer and the undoped InGaN layer have the same composition. By forming an InGaN / InGaN modulated doping layer of the same composition between the contact layer and the active region, it is possible to reduce the strain generated in the active region while preventing the process time lengthening, and to improve the crystallinity of the quantum well to recombine the carrier You can increase the rate.

Light Emitting Diodes, Superlattices, Contact Layers, InGaN

Description

LIGHT EMITTING DIODE HAVING MODULATION DOPED LAYER

The present invention relates to a light emitting diode, and more particularly to a light emitting diode having a modulation doping layer.

In general, nitride-based semiconductors are widely used in ultraviolet, blue / green light emitting diodes, or laser diodes as light sources for full color displays, traffic lights, general lighting, and optical communication devices. The nitride-based light emitting device includes an active region of an InGaN-based multi-quantum well structure located between n-type and p-type nitride semiconductor layers, and generates light based on the recombination of electrons and holes in the quantum well layer in the active region. To release.

In the conventional nitride compound semiconductor, since 11% lattice mismatch exists between GaN and InN, strong strain is generated at the interface between the quantum well and the quantum barrier in the InGaN-based multi-quantum well structure. This strain causes a piezoelectric field in the quantum well, leading to a decrease in internal quantum efficiency. In particular, in the case of the green light emitting diode, since the amount of In contained in the quantum well increases, the internal quantum efficiency is further reduced by the piezoelectric field.

On the other hand, the strain generated in the multi-quantum well structure is affected by the n-type nitride semiconductor layer adjacent to the active layer. The larger the mismatch of the lattice constant between the n-type nitride semiconductor layer, such as the n-type contact layer and the quantum well layer, the greater the strain in the active region.

In order to reduce the strain generated in the active region, a technique of forming a superlattice structure in which a first nitride semiconductor layer and a second nitride semiconductor layer having different compositions are alternately stacked between the n-type GaN contact layer and the active layer is used. . However, in the case of forming a superlattice structure composed of nitride semiconductor layers having different compositions between the n-type contact layer and the active layer, the growth conditions, for example, temperature and gas flow rate of each layer are different, which leads to complicated process and longer process time. There is a problem.

The problem to be solved by the present invention is to provide a light emitting diode that can alleviate the strain caused in the active region while preventing a long process time.

In order to solve the above problems, the light emitting diode according to the embodiments of the present invention is an n-type contact layer, a p-type contact layer formed on the n-type contact layer, interposed between the n-type contact layer and the p-type contact layer And an active region of a multi-quantum well structure including an InGaN layer, and a modulation doping layer interposed between the n-type contact layer and the active region. Meanwhile, the modulation doped layer has a structure in which an n-type impurity doped InGaN layer and an undoped InGaN layer are alternately stacked, and the n-type impurity doped InGaN layer and the undoped InGaN layer have the same composition. By forming an InGaN / InGaN modulation doping layer having the same composition between the contact layer and the active region, it is possible to alleviate the strain generated in the active region while preventing the process time lengthening, and improve the crystallinity of the quantum wells to recombine the carrier You can increase the rate.

The modulation doping layer may be formed in 7 to 15 cycles. In the case of less than 7 cycles, the effect of mitigating strain caused by the modulation doped layer in the active region is insignificant.

It is preferable that the In content of each layer in the modulation doped layer is smaller than the InGaN layer in the active region. Accordingly, charges can be confined in the active region, thereby improving the recombination rate of electrons and holes.

The n-type impurity doped InGaN layer may contact the active region in the modulation doped layer. In addition, the doping concentration of the n-type impurity doped InGaN layer may be relatively higher than the impurity doping concentration of the n-type contact layer. Accordingly, electrons can be smoothly injected into the active region from the modulation doped layer.

According to embodiments of the present invention, by forming an InGaN / InGaN modulation doping layer having the same composition between the contact layer and the active region, strain generated in the active region can be alleviated while preventing the process time from lengthening, and the quantum well By improving the crystallinity of the carrier can increase the recombination rate of the carrier. As a result, it is possible to provide a light emitting diode with improved luminous efficiency.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; The following embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. In the drawings, widths, lengths, thicknesses, and the like of components may be exaggerated for convenience. Like numbers refer to like elements throughout.

1 is a cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

Referring to FIG. 1, the light emitting diode includes a substrate 21, an n-type contact layer 27, a modulation doping layer 28, an active region 29 having a multi-quantum well structure, and a p-type contact layer 33. do. In addition, the nuclear layer 23 and the undoped GaN layer (u-GaN, 25) may be interposed between the substrate 21 and the n-type contact layer 27, the active region 29 and the p-type contact layer A p-type cladding layer 31 may be interposed between 33. In addition, the transparent electrode 35 and the p-electrode 37 may be positioned on the p-type contact layer 33, and the n-electrode 39 may be positioned on the n-type contact layer 27.

The substrate 21 is a substrate for growing a gallium nitride-based semiconductor layer, but is not particularly limited, such as sapphire, SiC, spinel, but preferably, as shown, may be a patterned sapphire substrate (PSS).

The nuclear layer 23 may be formed of (Al, Ga) N at a low temperature of 400 ~ 600 ℃ to grow u-GaN (25) on the substrate 21, preferably formed of AlN. The nuclear layer may be formed to a thickness of about 25nm.

The u-GaN layer 25 is a layer for alleviating the occurrence of defects such as dislocations between the substrate and the n-type contact layer 27, and is grown at a relatively high temperature. The n-type contact layer 27 is a layer on which the n-electrode 39 is formed, and may be doped with n-type impurities such as Si or Ge.

The modulation doped layer 28 has a structure in which n-type impurity doped, for example Si-doped InGaN layer 28a and undoped InGaN layer 28b are alternately stacked. These InGaN layers 28a and 28b have the same composition but differ only in the presence or absence of n-type impurity doping. Thus, the modulation doped layer 28 can be grown by repeating the supply and interruption of a source gas of Si, such as silane, continuously at the same temperature.

Si doped in the InGaN / InGaN modulation doping layer 28 has a smaller atomic size than In or Ga, thereby relieving stress induced in InGaN and also preventing the potential induced in the lower layer from being transferred to the upper layer. Accordingly, crystallinity of the active region 29 formed on the modulation doped layer 28 can be improved, and strain can be reduced. The modulation doping layer 28 may be formed in 7 to 15 cycles. If the modulation doping layer 28 is less than 7 cycles, the modulation doping layer has a weak effect of mitigating strain induced in the active region. Not desirable

On the other hand, the thickness of each layer in the modulation doping layer 28 may be formed to a thickness similar to the thickness of 3 ~ 80nm, or the thickness of the quantum barrier layer in the multi-quantum well structure. In addition, the overall thickness of the modulation doping layer 28 is not particularly limited, but if excessively thick, Vf may increase, so that the total thickness of the active region is preferably about 100 to 150 nm or less.

The In composition ratio of the modulation doped layer 28 is preferably less than the In composition ratio in the InGaN quantum well layer. In this case, the charge can be well confined in the active region, thereby improving luminous efficiency.

In addition, the n-type impurity doped InGaN layer 28a may be in contact with the active region 29 in the modulation doped layer 28. Since the InGaN layer 28a doped with impurities contacts the active region, electrons can be smoothly injected from the modulation doped layer 28 into the active region 29. In addition, the doping concentration of the n-type impurity doped InGaN layer 28a may be relatively higher than the impurity doping concentration of the n-type contact layer 27. Accordingly, an increase in resistance of the modulation doped layer 28 may be prevented, and electron injection efficiency into the active region may be increased by electrons generated therein.

The active region 29 has a multi-quantum well structure in which a quantum barrier layer and a quantum well layer are alternately stacked, and the quantum well layer includes an InGaN layer. The In composition ratio in the InGaN quantum well layer is determined by the desired light wavelength.

Meanwhile, the p-type cladding layer 31 may be formed of conventional AlGaN, and the p-type cladding layer 33 may be formed of GaN.

In addition, a transparent electrode 35 such as Ni / Au or indium tin oxide (ITO) is formed on the p-type contact layer 33, and the p-electrode 37 is formed thereon, for example, by a lift-off process. Can be. In addition, an n-electrode 39 such as Ti / Al may be formed on the n-type contact layer 27 by a lift off process.

(Example)

A light emitting diode having the structure as shown in FIG. 1 was manufactured. That is, after growing 25 nm of the AlN nucleus layer 23 on the patterned sapphire substrate 21, the u-GaN layer 25 is 2 μm thereon, and the n-type contact layer on the u-GaN layer 25 ( 27) was grown by 4 mu m, and the Si doped InGaN layer 28a and the undoped InGaN layer 28b were grown 15 cycles each with a thickness of 3 nm to form a modulation doped layer 28. After growing an active region of a multi-quantum well structure having a total thickness of about 110 nm, a p-type AlGaN cladding layer 31 and a p-type GaN contact layer 33 were grown to fabricate a light emitting diode according to the present embodiment.

(Comparative Example)

A light emitting diode according to the prior art was manufactured by forming an active region directly on the n-type contact layer 27 without forming the modulation doped layer 28. This light emitting diode has the same structure as the light emitting diode of the embodiment except that there is no modulation doping layer.

Table 1 summarizes the characteristics of the light emitting diodes according to the above Examples and Comparative Examples.

Wavelength (@ 20 mA)
(nm) Vf (@ 1uA)
(V) Vf (@ 20mA)
(V) Ir (@ -5V)
(mA) Po (@ 20 mA)
(mW) Po (@ 80 mA)
(mW)
Comparative example 452.02 2.16 2.91 0.240 15.36 49.26 451.81 2.19 2.92 0.207 15.40 48.98 Example 450.00 2.22 2.92 0.188 16.00 51.10 449.27 2.21 2.93 0.200 16.04 51.32

As can be seen from Table 1, the adoption of the Si-InGaN / u-InGaN modulation doping layer 28 shortens the peak wavelength of the emitted light and improves the light output. This is because the strain of the active region is relaxed by adopting the modulation doping 28 and the crystallinity of the active region is improved. On the other hand, with the modulation doped layer 28, the voltage at 1uA, i.e., the turn-on voltage, increased, and the reverse current at -5V decreased. The forward voltage did not show a significant change.

1 is a cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

Claims (5)

n-type contact layer; A p-type contact layer formed on the n-type contact layer; An active region interposed between the n-type contact layer and the p-type contact layer, the active region having a multi-quantum well structure including an InGaN layer; And It includes a modulation doping layer interposed between the n-type contact layer and the active region, The modulation doped layer has a structure in which an n-type impurity doped InGaN layer and an undoped InGaN layer are alternately stacked. The n-type impurity doped InGaN layer and the undoped InGaN layer have the same composition, The n-type impurity doped InGaN layer is in contact with the active region in the modulation doped layer, At least one n-type impurity doped InGaN layer in the modulation doped layer is higher than an impurity doping concentration of the n-type contact layer. The light emitting diode of claim 1, wherein the modulation doping layer has 7 to 15 cycles. The light emitting diode of claim 1, wherein an In content of each layer in the modulation doped layer is less than that of an InGaN layer in an active region. delete The light emitting diode of claim 1, wherein a doping concentration of the n-type impurity doped InGaN layer is higher than an impurity doping concentration of the n-type contact layer.

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