Patent Application
20050074044
This invention relates to radiation-emitting semiconductors.
Conventional semiconductor devices often have confinement layers of InAlGaP, between which an active layer is arranged. These confinement layers constitute barriers for charge carriers. The confinement layers serve to confine the charge carriers or at least increase their retention period within the active layer.
It is desirable that the charge carriers are as completely confined as possible or that their retention period within the active layer lasts as long as possible. Outside the active layer, charge carriers do not contribute significantly to the production of radiation.
Customarily, confinement layers and active layers are lattice matched, i.e., the adjacent layers have essentially the same lattice constant. An insufficient lattice match bears the possible risk of creating strain between the confinement layer and the active layer, as well as defects in the crystal lattice. Such defects can diminish the radiation effect, since they can favor the non-radiating recombination of charge carriers.
In lattice matched confinement layers of InAlGaP, the maximally achievable barrier height, i.e., the potential enery difference through which a charge carrier would need to travel to escape the active layer, e.g., the difference between the energy levels of the active and confinement layers is relatively low. Typically, the maximum barrier height, is attained with AlInP confinement layers. Because of the limited barrier height leakage currents of charge carriers can occur. Leaked currents of charge carriers do not contribute to the creation of radiation.
A closely related problem of the charge carrier confinement exists in radiation-emitting quantum well structures of InAlGaP. Confinement of the charge carrier here takes place in the quantum well or wells. A quantum well structure of InAlGaP contains multiple subsequent quantum well and barrier layers. As with the confinement layers, a potential problem is the limited height of the barriers in the case of lattice matched layers.
Radiation-emitting semiconductors using indium gallium aluminum phosphide (InAlGaP) and having improved charge carrier confinement are described.
In one aspect, a radiation-emitting semiconductor is described that has a two confinement layers. Between the confinement layers is a radiation-emitting active layer including InxAlyGa1-x-yP (0≦x≦1, 0≦y≦1, 0≦x+y≦1). At least one of the confinement layers includes one or more of InxAlyGa1-x-yPuN1-u (0≦x≦1, 0≦y≦1, 0≦x+y≦1 and 0≦u<1), BzInxAlyGa1-x-y-zPuN1-u (0≦x≦1, 0≦y≦1, 0<z≦1, 0≦x+y+z≦1 and 0≦u<1) or a II-IV semiconductor material.
In another aspect, a radiation-emitting semiconductor, including a radiation-emitting active layer is described. The radiation-emitting active layer includes InxAlyGa1-x-yP (0≦x≦1, 0≦y≦1, 0≦x+y≦1) with a quantum well structure having one or more barrier layers. The one or more barrier layers include InxAlyGa1-x-yPuN1-u (0≦x≦1, 0≦y≦1, 0≦x+y≦1 and 0≦u<1), BzInxAlyGa1-x-y-zPuN1-u (0≦x≦1, 0≦y≦1, 0<z≦1, 0≦x+y+z≦1, 0≦u<1) or a II-IV semiconductor material.
In another aspect, a radiation-emitting semiconductor is described that has a two confinement layers and a radiation-emitting active layer having a quantum well structure. At least one of the confinement layers includes one or more of InxAlyGa1-x-yPuN1-u (0≦x≦1, 0≦y≦1, 0≦x+y≦1 and 0≦u<1), BzInxAlyGa1-x-y-zPuN1-u (0≦x≦1, 0≦y≦1, 0<z≦1, 0≦x+y+z≦1 and 0≦u<1) or a II-IV semiconductor material. Between the confinement layers is the radiation-emitting active layer. The radiation-emitting emitting active layer includes InxAlyGa1-x-yP (0≦x≦1, 0≦y≦1, 0≦x+y≦1) with a quantum well structure having one or more barrier layers. The one or more barrier layers include InxAlyGa1-x-yPuN1-u (0≦x≦1, 0≦y≦1, 0≦x+y≦1 and 0≦u<1), BzInxAlyGa1-x-y-zPuN1-u (0≦x≦1, 0≦y≦1, 0<z≦1, 0≦x+y+z≦1, 0≦u<1) or a II-IV semiconductor material.
1. In any of the described structures, the II-IV semiconductor material can include ZnxMg1-xSySe1-y (0≦x≦1, 0≦y≦1), ZnxMgyCd1-x-ySuSe1-u (0≦x≦1, 0≦y≦1, 0≦x+y≦1, 0≦u≦1), ZnxMgyCd1-x-yTe (0≦x≦1, 0≦y≦1, 0≦x+y≦1), ZnxMgyCd1-x-ySe (0≦x≦1, 0≦y≦1, 0≦x+y≦1) or ZnxMgyCd1-x-yS (0≦x≦1, 0≦y≦1, 0≦x+y≦1).
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
Semiconductor bodies having active layers and confinement layers containing InAlGaP are described.
In a first implementation, a radiation-emitting semiconductor has a radiation-emitting active layer of InxAlyGa1-x-yP 0≦x≦1, 0≦y≦1, 0≦x+y≦1) (indium aluminum gallium phosphide, InAIGaP). The radiation layer is arranged between first and second confinement layers. At least one of the confinement layers includes InxAlyGa1-x-yPuN1-u (0≦x≦1, 0≦y≦1, 0≦x+y≦1, and 0≦u<1) (indium aluminum gallium phosphorus nitride, InAlGaPN), BzInxAlyGa1-x-y-zPuN1-u (0≦x≦1, 0≦y≦1, 0<z≦1, 0≦x+y+z≦1, and 0≦u<1) (boron indium aluminum gallium phosphorus nitride, BInAlGaPN), or a II-IV semiconductor material. The II-IV semiconductor material can be ZnxMg1-xSySe1-y (0≦x≦1, 0≦y≦1) (zinc magnesium silicon selenide, ZnMgSSe), ZnxMgyCd1-x-ySuSe1-u (0≦x≦1, 0≦y≦1, 0≦x+y≦1, 0≦u≦1) (zinc magnesium cadmium silicon selenide, ZnMgCdSSe), ZnxMgyCd1-x-yTe (0≦x≦1, 0≦y≦1, 0≦x+y≦1) (zinc magnesium cadmium telluide, ZnMgCdTe), ZnxMgyCd1-x-ySe (0≦x≦1, 0≦y≦1, 0≦x+y≦1) (zinc magnesium cadmium selenide, ZnMgCdSe) and ZnxMgyCd1-x-yS (0≦x≦1, 0≦y≦1, 0≦x+y≦1) (zinc magnesium cadmium silicide, ZnMgCdS). Other II-IV semiconductor materials can also be suitable for the confinement layers, such as wide band gap semiconductors. At least one of the confinement layers can contain a quaternary compound, i.e., a compound with four elements, where x>0, y>0, and x+y<1. The confinement layers can also include a quinary compound with the value u>0. The first and second confinement layers can have the same composition.
With the materials described, i.e., InAlGaPN, BInAlGaPN, or a II-IV semiconductor material, a confinement layer can be constructed for an active layer of InAlGaP that has a greater barrier height than an InAlGaP confinement layer or an AlInP confinement layer. This can result in an efficient confinement of the charge carriers or, to a particularly low leakage current.
The confinement layer or confinement layers can be lattice matched. Two adjacent semiconductor layers having a crystal lattice with essentially the same lattice constant are lattice matched. Lattice matching can prevent defects between layers. Mismatched lattices can induce stress in the semiconductor layers. With the materials mentioned, the confinement layers can have a greater barrier height, while at the same time can be lattice matched to the active layer.
However, lattice matching of the confinement layers may not be necessary. Because of the potentially greater barrier height of the confinement layers, lattice matching can be dispensed with and the possible resulting, usually tensile, strain between the active layer and the confinement layers, can be tolerated. An increase of the radiation effect can be attained in this case nonetheless, i.e., the strain induced losses are compensated by the improved confinement of the charge carriers.
In one variation of the implementation, the first and/or second confinement layers are arranged at a distance from the active layer such that the distance is smaller than the diffusion length. The diffusion length is the measure for the spatial location area of the charge carrier during its average lifetime. In this manner, the largest possible portion of the charge carriers injected into the active layer can be contained by the confinement layers. Thus, locating confinement layers a distance from the active layer that is less than the diffusion length can further increase the radiation efficiency.
In a second implementation, a radiation-emitting semiconductor has a radiation-emitting active layer including InxAlyGa1-x-yP (0≦x≦1, 0≦y≦y≦1, 0≦x+y≦1) with a quantum well structure having one or more barrier layers. At least one of the barrier layers contains InxAlyGaz-x-yPuN1-u (0≦x≦1, 0≦y≦1, 0≦x+y≦1, and 0≦u<1), BzInxAlyGa1-x-y-zPuN1-u (0≦x≦1, 0≦y≦1, 0<z≦1, 0≦x+y+z≦1 and 0≦u<1) or a II-IV semiconductor material.
Again, with the materials InAlGaPN and BInAlGaPN, or a II-IV semiconductor material, such as ZnMgSSe, ZnMgCdSSe, ZnMgCdTe or ZnMGCdS, in the active layer, a greater barrier height can be achieved than with InAlGaP barrier layers. Thus, a more efficient confinement of the charge carriers can be achieved. Here, the confinement is in the individual quantum wells within the active layer.
As in the first implementation, with regard to an efficient charge carrier confinement, the quantum well or quantum wells can be enclosed on both sides with barrier layers that contain InAlGaPN, BInAlGaPN, or a II-IV semiconductor material.
In a third implementation, a radiation-emitting semiconductor includes an active layer having a quantum well structure that is enclosed on one or both sides by confinement layers. In this implementation, both the barrier layer or barrier layers of the quantum well structure in the active layer and at least one, or both, confinement layers contain InAlGaPN, BInAlGaPN, or a II-IV semiconductor material, such as ZnMgSSe, ZnMgCdSSe, ZnMgCdTe or ZnMgCdS. The barrier layers and the active layer can be of the same composition.
Referring to
The series of semiconductor layers 7 comprises a radiation-emitting active layer 2 of InAlGaP. The active layer 2 can either consist of InAlGaP or contain InAlGaP. In the latter case, the active layer can also contain additional materials. The active layer 2 can be substantially free of any nitride compound semiconductor, e.g., InxAlyGa1-x-yPuN1-u (0≦x≦1, 0≦y≦1, 0≦x+y≦1 and 0≦u<1). In one variation of the first implementation, the active layer consists of one or more layers of InAlGaP.
The active layer can be multi-layered, where only portions of the active layer include InAlGaP and/or the InAlGaP composition differs in various parts of the active layer. This also relates to quantum well structures, which shall be explained in more detail below.
Lattice matched confinement layers 3, 4 can be located on either side of the active layer 2. At least one of the two confinement layers 3,4 can contain InAlGaPN, BInAlGaPN, or a II-IV semiconductor material, such as ZnMgSSe, ZnMgCdSSe, ZnMgCdTe or ZnMgCdS. Both confinement layers can contain InAlGaPN, BInAlGaPN, or a II-IV semiconductor material. The confinement layers can have the same composition to obtain a desired charge carrier confinement.
The confinement layers 3, 4 can increase the barrier height with regard to the active layer 2 and, thus, improve the charge carrier confinement. This results in low leakage currents and to an efficient radiation effect.
The confinement layers 3, 4 need not be immediately adjacent to the active layer 2. The distance between confinement layers 3, 4 and active layer 2 can be smaller than the diffusion length of the charge carriers in the active layer. When the distance from the active layer is greater than the diffusion length, the number of charge carriers injected into the active layer decreases. Correspondingly, the effectiveness or efficiency of the confinement layers decreases. The persisting barrier height can then contain only the remaining charge carriers that are injected into the active layer.
Referring to
In this second application example, the active layer 2 is designed as a quantum well structure 5 in the form of a double quantum well (DQW) with three barrier layers 6 and two quantum well layers 8 of InAlGaP, each quantum well layer arranged between two barrier layers 6. Pure InAlGaP layers can be used to form the quantum well layers 8. Other quantum well structures can be used, such as simple quantum well structures or multiple quantum well structures with more than two quantum well layers.
The barrier layers 6 can contain InAlGaPN, BInAlGaPN, or a II-IV semiconductor material, such as, ZnMgSSe, ZnMgCdSSe, ZnMgCdTe or ZnMgCdS. This enables greater barrier heights than are typically obtained with standard InAlGaP barrier layers. Greater barrier heights can lead to an improvement of the charge carrier confinement as well as increased efficiency of the radiation effect.
Referring to
The improved charge carrier confinement, both in the active layer 2 as a whole and in the individual quantum well layers 6, results in a particularly effective construction element.
The barrier heights of the confinement layers 3, 4 do not have to correspond to the barrier heights of the barrier layers 6. If the confinement layers 3,4 and the barrier layers have a different composition, the barrier height of the confinement layers can exceed that of the barrier layers. Thus, a two-fold, staged type of charge carrier confinement can be obtained.
The series of semiconductor layers 7 can contain additional layers. A buffer layer can be arranged between the substrate 1 and the active layer 2 or the first confinement layer. One or more contact layers can be formed on the side of the active layer opposite from the substrate 1. Furthermore, the active layer, or the active layer together with the confinement layers, can be arranged between two coat or cover layers. In a semiconductor laser application, a separate wave guide or optical confinement layers can be arranged on either side of the active layer or on either side of the active layer and the confinement layers, as described above.
In a variation of the above described implementations, a substrate is not used to form the above described semiconductors. In a thin-film construction element, the substrate can be replaced by a series of semiconductor layers. A thin-film construction element can be an element containing a series of semiconductor layers that have been epitaxially grown onto a growth substrate. The growth substrate can be at least in part separate from the series of semiconductor layers. For mechanical stabilization, the series of semiconductor layers can be installed on a carrier.
The semiconductor can be designed as a light emission diode, e.g., as an LED or laser diode. With these elements, a significant increase in efficiency can be achieved. In laser diodes, the charge carrier confinement can decrease the threshold current density.
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10345412.8 | Sep 2003 | DE | national |
| 10355962.0 | Dec 2003 | DE | national |
