KR101462238B1 - High-efficiency blue InGaN/GaN quantum-well light-emitting diodes with saw-like later - Google Patents

Abstract

The present invention relates to a high efficiency blue InGaN / GaN quantum well LED with a sawtooth layer wherein the luminescent properties of the sawtooth InGaN / GaN quantum well (QW) LEDs are investigated using multi-band effective mass theory, The spontaneous emission peak of the QW structure is improved compared to the conventional quantum well (QW) structure because the matrix element is improved in the inclusion of the sawtooth layer, and also in the case of the sawto-type quantum well (QW) structure, Since the internal field effect is reduced due to the polarization, the transition energy becomes a weak function of the carrier density and the built-in electric field effect can be reduced. In addition, a method using a substrate having a non-directional (0001) orientation or an InGaN well , A method of injecting an AlGaNδ layer into a thick InGaN well and a method of using a four layer AlInGaN barrier to reduce the internal field effect, Ground quantum well (QW) is a useful invention that has particular advantages for non room (非 正方) achieve high efficiency of the quantum well (QW) structure by a method similar to the preparation of the structure.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high efficiency blue InGaN / GaN quantum well LED having a sawtooth layer,

The present invention relates to a high efficiency blue InGaN / GaN quantum well LED having a sawtooth layer, and more particularly to a light emitting diode (LED) having a luminescent characteristic of a sawtooth InGaN / GaN quantum well (QW) Shows that the spontaneous emission peak of a saw-like quantum well (QW) structure is improved as compared to that of a conventional quantum well (QW) structure, as compared with the luminescence characteristics of a quantum well (QW) LED of InGaN / GaN. The electron wave function is determined by the fact that the hole wave function moves to the left with inclusion of the saw-like layer while it is almost unchanged, and as a result the matrix element is a high-efficiency blue (blue) InGaN / GaN quantum well LED.

In recent years, quantum wells (QWs) based on wide band gap (WZ) GaN have attracted much attention due to potential device applications in electronic and optoelectronic devices (Non-Patent Document 1) very important. However, quantum wells based on (0001) direction wurtzite (WZ) GaN are known to have large internal fields due to strain-induced piezoelectric (PZ) and spontaneous polarization. Induced spatial separation between electrons and hole waves, and the emission recombination is greatly reduced (Non-Patent Documents 2 and 3). As a result, the luminescent recombination rate and the optical gain of these quantum well (QW) structures are significantly reduced and the high critical current density (Jth ~ 1.5-6kA / cm2, λ = 425 - 482 nm) (Non-Patent Document 4).

Other approaches to overcome this drawback have been proposed in order to reduce the built-in electric field effects, which are either a method using a substrate with a non-directional (0001) orientation, a method using an In-rich InGaN well (Non-Patent Document 9) and a method of using a four-layered AlInGaN barrier (Non-Patent Documents 10, 11, and 12), a method of injecting an AlGaN? Layer into a thick InGaN well . Since the growth process is almost the same as that of the conventional structure, the possibility of crystal defects does not increase so much. Recently, a non-square InGaN / GaN system having a two- and three-layer staggered quantum well (QW) (Non-Patent Document 13). Since this structure can be obtained by a method similar to the fabrication of a three-layer staggered quantum well (QW) structure, the present process of this non-square quantum well (QW) structure, which has a saw- Investigation of the optical properties of InGaN / GaN quantum well (QW) structures will be interesting.

In the present invention, the emission characteristics of saw-like InGaN / GaN quantum well (QW) light emitting diodes (LEDs) are investigated, and these results are compared with conventional InGaN / GaN quantum well (QW) light emitting diodes (LEDs). The self-consistency (SC) band structure and the wave function can be obtained by solving the Schöndinger equation for electrons, the 3 × 3 Hamiltonian discharge equation for holes, and the equation for Poisson's equation repeatedly (Non-Patent Documents 14 and 15 ). The In component in the well is selected to provide a transition wavelength of 440 nm at a carrier density of N _2D = 10 x 10 ¹² cm ^-2 .

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The present invention has been made to solve the various drawbacks and problems caused by the LED of the InGaN / GaN quantum well (QW) structure, and it is an object of the present invention to provide a high efficiency blue light emitting diode having a sawtooth layer capable of reducing the built- InGaN / GaN quantum well LEDs.

Another object of the present invention is to provide a method of using a substrate having a non-directional (0001) orientation, a method of using an InGaN well rich in InGaN, a method of injecting an AlGaNδ layer into a thick InGaN well, Efficient blue InGaN / GaN quantum well LED having a sawtooth layer with reduced internal field effect by adopting a method using an AlInGaN barrier.

It is a further object of the present invention to provide a method of forming a high-efficiency (QW) structure having a saw-like layer that achieves high efficiency of a non-square quantum well (QW) structure by a method similar to the fabrication of a three-layer staggered quantum well And a blue InGaN / GaN quantum well LED.

In order to achieve the above object, a high-efficiency blue InGaN / GaN quantum well LED having a sawtooth layer according to the present invention includes a sawtooth InGaN (GaN) layer having a thickness of 1.0, 0.5 and 1.0 nm / GaN quantum well (QW) structure.

The present invention can reduce the built-in electric field effect, and can be applied to a method using a substrate having a non-directional (0001) orientation, a method using an InGaN well with an extremely thin InGaN, a method of injecting an AlGaNδ layer into a thick InGaN well, (QW) structure by a method similar to the fabrication of a three-layer staggered quantum well (QW) structure by employing a method using a quaternary AlInGaN barrier to reduce the internal field effect Which is a significant advantage of achieving high efficiency.

Fig. 1 is a graphical representation of a localized center of a sawtooth InGaN / GaN quantum well (QW) with an In component in the InGaN layer to the right of (a) z = 0.06, (b) z = 0.09, A potential profile and wave function of the first conduction server band (C1), a graph showing the potential profile and wave function of the first valence subband (HH1), respectively,
Fig. 2 (a) shows the peak transition wavelength as a function of the sheet carrier density, Fig. 2 (b) is a graph showing the optical matrix elements as a function of the In component of the right InGaN layer of the InGaN / GaN quantum well (QW)
3 (a) shows the potential profile and first conduction in the local center for the ground state of the three InGaN layer saw-top InGaN / GaN quantum well (QW) structures having In components of 0.19, 0.14 and 0.09, respectively, A graph showing the wave function of subband C1 and valence subband HH1,
Fig. 4 (a) shows the peak transition wavelength as a function of the sheet carrier density of a saw-shaped InGaN / GaN quantum well (QW) structure having In components of 0.19, 0.14 and 0.09, (QW) structure of a top InGaN / GaN quantum well (QW) structure having a structure of a conventional InGaN / GaN quantum well (QW) structure with N _2D = 10 x 10 ¹² cm ^-2 sheet carrier density, And the natural emission coefficient.

는 하기 수학식 1로 주어진다(비특허문헌 16, 17).Non-Markovian spontaneous emission spectrum with multibody effect

Is given by the following equation (Non-Patent Documents 16 and 17).

는 광학 전기장의 방향에서의 단위벡터, 또한, |M_lm|² 은 응력 변형된 양자우물(strained QW) 내 모멘텀 매트릭스 요소(momentum matrix element)를 나타낸다.Where ω is the angular frequency, μ ₀ is the vacuum permeability, ε is the dielectric constant, and σ = U (or L) is the upper (lower) block for the effective mass Hamiltonian Where e is the charge on an electron, m ₀ is the electron mass, k _∥ is the size of the in-plane wave vector in the quantum well (QW) plane, and Lw Well thickness,

Is the unit vector in the direction of the optical electric field, and | M _lm | ² represents a momentum matrix element in a strained QW.

과

은 전도대(conduction band) 상태와 가전자대(valence band) 상태에 대한 페르미 함수(Fermi functions)를 각각 나타내고,

는 플랭크 상수(Plank constant)를 나타낸다. 지수 l과 m 은 전도대 내의 전자 상태와 가전자대 내의 무거운 정공(가벼운 정공) 부대역(subband) 상태를 각각 나타낸다.And,

and

Denotes the Fermi functions for the conduction band state and the valence band state, respectively,

Represents a Plank constant. The exponents l and m represent the electron state in the conduction band and the heavy hole (light hole) subband state in the valence band, respectively.

는 전자와 전공 사이의 환치(renormalization)된 전이에너지이다. 여기서

는 물질의 밴드갭,△E _SX 와 △E _CH는 각각 밴드갭 환치(renormalization)에 대한 스크린된 교류(SX; screened exchange)와 쿨롱-정공의 기여도이다(비특허문헌18). 지수

는 대간전이(帶間轉移) 확률의 여기(excitonic) 또는 쿨롱 증대에 대한 계정이다(비특허문헌 18, 19). 선형(line-shape) 함수는 간단한 비 마르코프(Markovian) 양자 역학(quantum)에 대한 가우시안(Gaussian) 모양이며, 수학식 2와 수학식 3으로 주어진다(비특허문헌 16, 17).Also,

Is the renormalized transition energy between electrons and electrons. here

Is the bandgap of the material, DELTA E _SX and DELTA E _CH are the screened exchange (SX) and coulomb-hole contribution to band gap renormalization, respectively (non-patent document 18). Indices

Is an account for the excitonic or coulone enhancement of the interstage transition probability (Non-Patent Documents 18 and 19). The line-shape function is a Gaussian shape for a simple Markovian quantum, given by Equations 2 and 3 (Non-Patent Documents 16 and 17).

에 의해 얻을 수 있다. 원자가 밴드의 홀파 기능은 주로 왼쪽 InGaN 층에 국한되어 있다. 다른 밴드에서 전도대의 전자 파동함수는 우물에서 세 InGaN 층에 국한되어 있다. 따라서, 그것은 전자 파동함수의 피크 위치, 가능하면 왼쪽 InGaN 근처에 전자 및 홀 파동함수 사이의 오버랩을 증가 할 수 있도록 하는 것이 바람직하다. 전자 파동함수의 정상 위치는 오른쪽 InGaN 층의 In 성분이 감소할 때 왼쪽 InGaN 층으로 이동한다. 그러나, 아래 도면과 같이 동시에 440nm보다 짧은 파장 전이를 제공한다.Fig. 1 is a graphical representation of a localized center of a sawtooth InGaN / GaN quantum well (QW) with an In component in the InGaN layer to the right of (a) z = 0.06, (b) z = 0.09, , The potential profile and wave function of the first first conduction-server band (C1), the potential profile of the first valence subband (HH1), and the wave function, respectively, with three InGaN layers at the saw- exist. Their thickness is 1.0, 0.5, and 1.0 nm, respectively, moving from left to right. In the left two layers, the In components are 0.19 and 0.14, respectively (Non-Patent Document 21). The inner field F of the layers is defined as the periodic boundary condition that runs through all layers where the sum includes the barrier layer and l represents the thickness of the layer

Lt; / RTI > The doping function of the valence band is mainly limited to the left InGaN layer. In other bands, the electron wave function of the conduction band is limited to the three InGaN layers in the well. Therefore, it is desirable to be able to increase the overlap between the electron wave function and the hole wave function at the peak position of the electron wave function, possibly near the left InGaN. The normal position of the electron wave function moves to the left InGaN layer when the In component of the right InGaN layer decreases. However, it provides a wavelength transition shorter than 440 nm at the same time, as shown in the figure below.

Fig. 2 (a) shows the peak transition wavelength as a function of the sheet carrier density, and Fig. 2 (b) shows the optical matrix element as a function of the In component of the right InGaN layer in the sawtooth InGaN / GaN quantum well (QW) structure. The transition wavelength and the optical matrix element can be obtained at N _2D = 10 x 10 ¹² cm ^-2 sheet carrier density. Since the peak position of the electron wave function is shifted to the left, the square light matrix element gradually increases with the decrease of the In component of the right InGaN layer.

However, a quantum well (QW) structure having fewer In components in the right InGaN layer has a shorter transition wavelength than a quantum well (QW) structure having a larger In component. This can be explained by the fact that the subband energy at the conduction band for a quantum well (QW) structure with fewer In components becomes larger due to the well width reduction effect. It can be seen that a quantum well (QW) structure with a transition wavelength of 440 nm can be obtained for the In component of 0.09 in the right InGaN layer.

3 (a) shows the potential profile at the local center for the ground state of the saw-top InGaN / GaN quantum well (QW) structure and the wave front of the first conduction subband (C1) and valence subband (HH1) Function. The three InGaN layers in the saw-top well have In components of 0.19, 0.14 and 0.09, respectively. The potential profile of a conventional InGaN / GaN quantum well (QW) structure represents a large spatial separation between electron and hole wave functions due to the large internal field in the well. However, the sawtooth InGaN / GaN quantum well (QW) structure shows that the spatial separation between electron and hole wave function is greatly reduced because the peak position of the electron wave function is shifted to the left.

Fig. 4 (a) shows the peak transition wavelength as a function of sheet carrier density, (b) shows the optical matrix elements, and (c) shows the spontaneous emission coefficients of the conventional and saw-top InGaN / GaN quantum well (QW) structures. The matrix element can be obtained at N _2D = 10 x 10 ¹² cm ^-2 sheet carrier density. The three InGaN layers in the saw-top well have In components of 0.19, 0.14 and 0.09, respectively. In the case of the conventional quantum well (QW) structure, since the internal field is screened by carriers filled at high carrier densities, the transition wavelength decreases rapidly with increasing carrier density. On the other hand, in the case of a saw-tooth quantum well (QW) structure, the transition energy is a weak function of the carrier density. This is due to the fact that piezorescence reduces internal field effects and spontaneous polarization in the well. Conventional quantum well (QW) structures represent small matrix elements due to large spatial separation between electron and hole wave functions. On the other hand, the optical matrix element is improved with respect to the saw-top InGaN / GaN quantum well (QW) structure. This is mainly determined by the fact that while the Hall wave function is almost invariant, the electron wave function moves to the left with the inclusion of the sawtooth layer. Peak position of the spontaneous emission spectrum is ^{_{N 2D = 10 × 10 12 ㎝}} - appears on the high carrier density of ² nearby 440nm. The spontaneous emission peak of the sawtooth type quantum well (QW) structure appears to be improved compared to the conventional quantum well (QW) structure. This is mainly due to the fact that matrix elements have improved inclusion of sawtooth layers.

While the present invention has been described with reference to the preferred embodiments, it is to be understood that the invention is not limited thereto and that various changes and modifications may be made therein without departing from the scope of the invention.

Claims (3)

The LED has a transition wavelength of 440 nm at a N _2D = 10 x 10 ¹² cm ^-2 sheet carrier density and has a larger optical matrix element size than conventional InGaN / GaN quantum well LEDs;
Moving from left to right in the quantum well (QW) and having thicknesses of 1.0, 0.5, and 1.0 nm, respectively;
Wherein the In component in the InGaN / GaN quantum well (QW) structure is in the range of 0.15 to 0.26. A high efficiency blue InGaN / GaN quantum well LED having a sawtooth layer. delete delete

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