JPH0712101B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] According to the present invention, in a quantum well laser, carrier injection efficiency is improved by forming a high concentration carrier scattering center by atomic plane doping of impurities in a quantum well layer. It is a thing.

[Industrial application field]

The present invention relates to a semiconductor light emitting device, and more particularly, to an improved structure for reducing the threshold current and improving the efficiency of a quantum well semiconductor laser.

Optical communication and other systems that use light as a medium for information signals are being advanced and diversified, and semiconductor light emitting devices, especially lasers, which play an important role as light sources, are further improved in characteristics such as efficiency. Is strongly requested.

[Conventional technology]

Many semiconductor lasers that have been conventionally used have a stripe-shaped active layer having an energy band cap corresponding to the wavelength of light of interest, and the active layer is sandwiched between semiconductor layers having a large energy band cap and a small refractive index to form a carrier. Further, light is confined to form a resonator, and carriers injected into the active layer are excited to cause laser oscillation.

If the quantum well type potential is formed by setting the thickness of the active layer of the semiconductor laser to be equal to or less than the de Broglie wavelength of the carrier, the carrier motion in the thickness direction is quantized.
In the dimensional state, the energy level becomes stepwise, and the density of states of carriers in the energy level involved in the oscillation is significantly increased, and the oscillation threshold current density is significantly reduced.

The de Broglie wavelength of this carrier is, for example, about 30 nm in gallium arsenide (GaAs), and the thickness of the quantum well layer is often set to about 10 nm or less in order to sufficiently disperse the energy level of carriers, especially electrons.

FIG. 2 (a) is a schematic side sectional view showing a conventional example of a quantum well semiconductor laser, and FIG. 2 (b) is an energy band diagram thereof, which correspondence is indicated by the same symbol.

In this conventional example, 21 is an n-type GaAs semiconductor substrate and 22 is an n-type
GaAs buffer layer, 23 is aluminum gallium arsenide (AlGa
As) confinement layer, 24 is a quantum well layer made of GaAs, and 25 is p
Type AlGaAs confinement layer 26 is a p-type GaAs contact layer. After epitaxially growing these semiconductor layers, for example, zinc (Z
n) and other impurities to diffuse p-type AlGaAs
Aluminum (Al) atomic GaAs contained in the confinement layer 25
Diffusion between semiconductor layers such as diffusion into the quantum well layer 24 is performed to destroy the quantum well structure and form a confinement region 27. Reference numeral 30 is an insulating film, 31 is a p-side electrode, and 32 is an n-side electrode.

In the carrier injection into the GaAs quantum well layer 24 of this conventional example, holes are injected from the p-side electrode 31 to the p-type contact layer 2 as in a normal double hetero semiconductor laser in which the active layer is not quantized.
6, through the p-type AlGaAs confinement layer 25, and electrons from the n-side electrode 32, n-type semiconductor substrate 21, n-type buffer layer 22, n-type Al
This is done through the GaAs confinement layer 23.

[Problems to be solved by the invention]

In carrier injection from such a confined confining layer into the active layer, as the active layer becomes thinner, the probability of passage thereof increases and the injection efficiency decreases.

In particular, in quantum well lasers in which the active layer has a quantum thickness, the injection efficiency is extremely low. For example, GRIN-SCH (GRaded INd
ex waveguide Separate Confinement Heterostructur
e) Structures such as a structure that gives a gradient to the barrier height of the confinement layer in the vicinity of the interface with the quantum well layer have been proposed, but satisfactory injection efficiency cannot be achieved, and its improvement is strongly desired.

[Means for solving problems]

In the semiconductor light emitting device having a quantum well layer as an active layer, the above problem is solved by the semiconductor light emitting device according to the present invention having a layer in which impurities are atomically plane-doped in the quantum well layer.

[Action]

In the present invention, the probability of carriers passing through the quantum well layer is reduced by clonal scattering due to impurity ions, and the injection efficiency is improved.

However, in the conventional doping method in which impurities are three-dimensionally mixed in a semiconductor, for example, Ga
If the maximum concentration of Si semiconductor doped with Sirincon (Si) is about 5 × 10 ¹⁸ cm ⁻³ and the heterojunction interface with the confinement layer of the quantum well layer is doped,
In the confinement layer, the absorption of light by free carriers increases and the effect is diminished.

On the other hand, according to atomic plane doping, which introduces impurities into the semiconductor layer two-dimensionally, a high concentration of about 1 × 10 ¹⁹ cm ⁻³ or more can be obtained, and the impurity ions are introduced from the heterojunction interface of the quantum well layer. It is possible to suppress light absorption loss in the separated confinement layer.

Thus, the efficiency of carrier injection into the quantum well layer is increased, emission recombination is sufficiently performed, light absorption loss is suppressed, and the threshold current is reduced and the emission efficiency is improved.

In a multiple quantum well laser in which a single quantum well layer is provided and a plurality of quantum well layers are provided via a barrier layer, introduction of impurities according to the present invention should be carried out only in the selected quantum well layer. Is also possible.

〔Example〕

 The present invention will be specifically described below with reference to examples.

FIG. 1 (a) is a schematic side sectional view showing an embodiment in which the present invention is applied to a quantum well laser having a GRIN-SCH structure made of a GaAs / AlGaAs semiconductor material, and FIG. 1 (b) is an energy near the active region. It is a band diagram, and its correspondence is indicated by the same reference numeral.

In this embodiment, n having an impurity concentration of, for example, about 2 × 10 ¹⁸ cm ⁻³
The following semiconductor layers are sequentially grown on the type GaAs semiconductor substrate 1 by the molecular beam epitaxial growth method.
The impurity doping of each semiconductor layer other than is normal three-dimensional doping, and Si is used as a donor impurity and beryllium (Be) or the like is used as an acceptor impurity.

In the n-type confinement layer 3 on the substrate 1 side, the Al composition ratio X =
A region 3b graded from X = 0.7 to X = 0.18 toward the interface with the active layer 4 is provided on the 0.7 region 3a, and a similar grading region 5b is provided in the p-type confinement layer 5 on the active layer 4. The GRIN-SCH structure is formed by being provided.

The growth of the active layer 4 is carried out by growing the GaAs layer 4a having a thickness of 3 nm on the grading region 3b of the n-type confinement layer 3 with As and Ga beams, stopping the Ga beam and injecting the Si beam to a surface concentration of about 6 ×. 10 ¹² cm ^-2 Si atomic plane doping 4b
Then, the Si beam is stopped, and the GaAs layer 4c is grown again to a thickness of 3 nm.

Thus, as shown in FIG. 1B, the active layer 4 is sandwiched between the confinement layers 3 and 5 to form a quantum well structure having a width (thickness) of 6 nm, and the impurity concentration thereof is 1 × 10 5. ^It has reached ¹⁹ cm ^-3 .

The confinement region 7 is formed by interdiffusion of Al atoms or the like between the semiconductor layers by Zn diffusion in this semiconductor substrate, and the insulating film 1 is formed.
The laser element of the present embodiment is completed by arranging 0, p-side electrode 11 and n-side electrode 12, and through the steps such as cleavage.

The threshold currents of the above-described example and a comparative sample having the same structure as that of the comparative example in which the active layer is not doped are compared and measured, and in this example, the current density is reduced by about 10 to 20% with respect to the comparative sample. Was confirmed.

Although the atomic plane doping is one layer in this embodiment, the impurity concentration can be further increased by performing the atomic plane doping a plurality of times at intervals of, for example, about 1 to 2 nm.

In the above description, the active region is composed of a single quantum well layer, but the present invention is also applied to a multiple quantum well laser in which a plurality of quantum well layers are provided with a barrier layer in between, and the same effect is obtained. Obtainable. In this case, not all the quantum well layers are subjected to atomic plane doping,
Atomic plane doping may be performed only on some quantum well layers in consideration of the light absorption effect.

In the above description, the GaAs / AlGaAs semiconductor is used, but indium phosphide / indium gallium arsenide (phosphorus) (In
The same effect can be obtained by applying the present invention to a quantum well semiconductor laser using another semiconductor material such as P / InGaAs (P) system.

〔The invention's effect〕

As described above, according to the present invention, the efficiency of injecting carriers into the quantum well active layer is increased, emission recombination is sufficiently performed, and the threshold current is reduced and the emission efficiency is improved.

[Brief description of drawings]

1 (a) is a schematic side sectional view showing an embodiment of a quantum well laser according to the present invention, FIG. 1 (b) is an energy band diagram in the vicinity of its active region, and FIG. 2 (a) shows a conventional example. A schematic side sectional view, FIG. 2 (b) is an energy band diagram near the active region. In the figure, 1 is an n-type GaAs substrate, 2 is an n-type GaAs buffer layer, and 3 is an n-type
AlGaAs confinement layer, 4 is GaAs quantum well active layer, 4a and 4c
Is a non-doped GaAs layer, 4b is a Si atomic plane doping layer, 5 is a p-type AlGaAs confinement layer, 6 is a p-type GaAs contact layer, 7 is a confinement region, 10 is an insulating film, 11 is a p-side electrode, and 12 is an n-side. The electrodes are shown.

Claims (1)

[Claims] 1. A semiconductor light emitting device having a quantum well layer as an active layer, wherein a layer in which impurities are atomically plane-doped is provided in the quantum well layer.