Semiconductor element emitting light in ultraviolet range

FIELD: semiconductor emitting devices.

SUBSTANCE: proposed semiconductor element that can be used in light-emitting diodes built around broadband nitride elements of A^IIIB^V type and is characterized in ultraviolet emission range extended to 280 -200 nm has structure incorporating substrate, buffer layer made of nitride material, n contact layer made of Si doped nitride material, active layer with one or more quantum wells made of nitride material, barrier layer made of Mg doped Al_XGa_I-XN, and p contact layer made of Mg doped nitride material; used as nitride material for n contact layer is Al_yGa_I-yN in which 0.25 ≤ V ≤ 0.65; used as nitride material of active layer is Al_ZGa_{I Z}N_, where V - 0.08 ≤ Z ≤ V - 0.15; in barrier layer 0.3 ≤ X ≤ 1; used as nitride material in p contact layer is Al_wGa_{1 - w}N, where V ≤ W ≤ 0.7; active layer is doped with Si whose concentration is minimum 10¹⁹ cm^-3; width "d" of active layer quantum wells is 1 ≤ d ≤ 4 nm; molar fraction of Al on barrier layer surface next to active layer is 0.6 to 1 and further reduces through barrier layer width to its boundary with p contact layer with gradient of 0.02 to 0.06 by 1 nm of barrier layer thickness, barrier layer width "b" ranging within 10≤ b ≤ 30 nm.

EFFECT: enlarged ultraviolet emission range of semiconductor element.

1 cl, 1 dwg, 1 tbl

The invention relates to the field of semiconductor emitting devices, more particularly to led-based wide bandgap nitride compounds of the type A^IIIB^V.

Known semiconductor light-emitting element containing a substrate, a buffer layer, an n-contact layer with a high conductivity, doped silicon, the active layer including the structure of the multiple quantum wells, barrier layers and the p-contact layer, US 6515313.

This solution provides a reduction of the electric field generated by the polarization charges at the boundaries of layers with different composition, with the aim of improving the internal quantum efficiency, however, does not allow for effective radiation in the ultraviolet range.

Also known semiconductor element emitting light in the ultraviolet range, the structure of which sequentially includes a sapphire substrate, a buffer layer made of a nitride material (AlN), the n-contact layer made of nitride materials (GaN)doped with Si, an n-emitter layer made of AlGaN, an active layer of multiple quantum wells made of a nitride material (InGaN), a barrier layer made of AlGaN doped with Mg, and p-contact layer made of nitride materials (GaN)doped with Mg, US 2002149024.

In this design to increase the value of the quantum efficiency of the led, the proportion of aluminum nitride in the composition of the n-emitter layer is from 0 to 6%, and the thickness of this layer is from 50 to 300 nm; the doping and composition of the layers of the n-type and p-type adjacent to the active layer, provide the ratio of the concentrations of electrons and holes about 1.

This solution is taken as the prototype of the present invention.

However, this semiconductor element is suitable mainly for radiation with a wavelength of 380 nm and above. In the shorter-wavelength range of the device is a prototype unworkable due to the specific composition of the layers.

For element in the ultraviolet (280 nm or less) require the use of nitride compounds with high aluminium content. Increasing the energy barrier for electrons in the barrier layer with a high content of AlN prevents the penetration of electrons into the p-layers. However, the built-in electric field in the barrier layer of AlGaN also creates a potential barrier for holes, resulting in their concentration in the emitter near the active region is small. On the other hand, the injected holes can freely penetrate the n-layers, resulting in a dominant nonradiative recombination of carriers at high injection levels.

The basis of the present invention it is the task of expanding the range of ultraviolet radiation of the semiconductor element to 280-200 nm.

According to the image the structure, this task is solved by in the semiconductor element, sluchayem light in the ultraviolet range, the structure of which sequentially includes a substrate, a buffer layer made of a nitride material, an n-contact layer made of a nitride-based material doped with Si, an active layer on the one or more quantum wells made of a nitride material, a barrier layer made of Al_XGa_1-XN doped with Mg, and p-contact layer made of a nitride-based material doped with Mg as a nitride material of the n-contact layer used Al_YGa_1-YN, in which 0,25≤Y≤0,65, as a nitride material of the active layer used Al_ZGa_1-ZN, where Y-0,08≤Z≤Y is 0.15, the barrier layer is 0.3≤X≤1, as a nitride material of the p-contact layer used Al_WGa_1-WN, where Y≤W≤0,7, while the active layer is doped with Si a Si concentration not less than 10¹⁹cm^-3width "d" of quantum wells in the active layer is 1≤d≤4 nm, the mole fraction of Al on the surface of the barrier layer adjacent to the active layer is from 0.6 to 1, and further reduced by the thickness of the barrier layer to the boundary with the p-contact layer with a gradient from 0.02 to 0.06 to 1 nanometer thickness of the barrier layer, and the width "b" of the barrier layer is within a 10≤b≤30 nm.

The applicant is elem not identified sources, contains information about technical solutions, identical to the present invention, which allows to make a conclusion about its compliance with the criterion of "novelty".

The proposed construction of a gradient composition of the barrier layer (the mole fraction of Al on the surface of the barrier layer adjacent to the active layer is from 0.6 to 1 and then decreases across the thickness of the barrier layer to the boundary with the p-contact layer with a gradient from 0.02 to 0.06 to 1 nanometer thickness of the barrier layer provides increased concentration of holes on the border of the active layer, since the gradient of the composition of the barrier layer leads to a more distributed polarization p-doping near the active layer.

The negative gradient of the composition of the barrier layer relative to the direction of the crystallographic axis [0001] increases the efficiency of the led structure at low and moderate currents; a positive gradient of the composition of the barrier layer significantly increases the effectiveness of the structure at high currents.

The proposed width of the barrier layer is from 10 to 30 nm, firstly, increases the injection of holes into the active layer and, secondly, eliminate the relaxation of the stress in the semiconductor element due to cracking of the barrier layer.

To improve the spectral characteristics of the radiation in the optimized structure ogran which increases the width of the quantum well in the range of 1-4 nm, to get rid of the second electronic level in the quantum well, but not too much lower capture efficiency of carriers in quantum pit. Use as a nitride material of the n-contact layer Al_YGa_1-YN, where 0,25≤Y≤of 0.65, the value "X" is in the range from 0.3 to 1 in the material of the barrier layer Al_XGa_1-XN, used in the p-contact layer of Al_WGa_1-WN, where Y≤W≤0,7, doping the active layer with Si concentration of Si atoms is not less than 10¹⁹cm^-3provide effective radiation in the range 280-200 nm, because the potential energy of the charge carriers in the designed layers is sufficient for the radiation quanta with high energy.

The applicant has not found any sources of information containing data about the impact of an alleged distinguishing signs on achieved as a result of their implementation of the technical result. This, according to the applicant demonstrates compliance with this technical solution, the criterion of "inventive step".

The invention is illustrated in the drawing, which shows a diagram of the layer structure of the semiconductor element.

The semiconductor element in a specific implementation, all of the examples has a structure which includes in series:

the substrate 1 made of, SAP the Ira, thickness of 500 microns;

- a buffer layer 2 of AlN with a thickness of 20 nm;

- the n-contact layer 3 made of Al_YGa_1-YN, where Y=0,52, doped with silicon to a concentration of 5·10¹⁸cm^-3thickness of 2 microns;

- active layer 4 containing one quantum pit, made of Al_ZGa_1-ZN, where Z=0.42 and doped with silicon to a concentration of atoms of 10¹⁹cm^-3;

- barrier layer 5 doped with magnesium to a concentration of 10¹⁹cm^-3made of Al_XGa_1-XN;

the p-contact layer 6 made of Al_WGa_1-WN, where W=0,52 doped with magnesium concentration 5·10¹⁹cm^-3thickness of 100 nm.

The semiconductor element is a double-sided led heterostructure with a variable composition of the barrier layer, which allows to obtain the internal efficiency or constant at the level of 35-40% at current densities of 10 A/cm²or changing from 20 to 50% in a wider range of current densities between 1 and 1,000 A/cm²when the density of dislocations ˜10⁹cm^-2. It should be noted that the decrease of the density of dislocations in the structure leads to a sharp increase its internal efficiency. When the density of dislocations ˜10⁷cm^-2it is possible to obtain the internal quantum efficiency close to 100%.

Testing is heterostructure was grown on a sapphire substrate by the method of ISO-hydride epitaxy at subatmospheric pressure and temperatures from 1000 to 1100° With n-contact layers were legionares Si to a concentration of 5·10¹⁸cm^-3that was installed by using Sims (secondary ion mass spectrometry). The active layer was legionalla Si to a concentration of 2·10¹⁹cm^-3barrier and p-contact layers were legionares Mg to a concentration of 5·10¹⁹cm^-3.

After the growth process, the structure was subjected to ion etching to form a Mesa to a depth corresponding to the level n-contact layer. Further etched and the remaining parts of the structure were applied respectively n - and p-contacts, which is a multilayered metal compositions, respectively, Ti/Al/Pt/Au and Ni/Au. Contacts were vigilis in nitrogen atmosphere at a temperature of 850°C for 30 seconds.

Forth from patterns cut out the individual LEDs, which are mounted on the heat sink p-contact down and it was soldered gold electrodes for supplying electric current.

To study fluorescence characteristics of the LEDs used spectrometer HLCAS-12 with specially selected diffraction grating, allowing measurements in the ultraviolet spectral range. As detector we used a photomultiplier tube PMT-100. The signal from the photomultiplier via a digital voltmeter Is transferred to the computer for final processing./p>

Accurate measurements of the radiation intensity was not less than 0.02%.

To measure the external efficiency of the led used calibrated photodetector based on amorphous Si:H doped with hydrogen). The measurements were performed at a fixed geometry of the experiment, which allows to quantitatively compare the radiation of different samples.

The electroluminescence of the LEDs were measured at the output of the radiation through the sapphire substrate.

In examples 1-7, the width of the quantum well is from 1 to 4 nm, the width of the barrier layer ranges from 10 to 30 nm, the mole fraction of aluminum in the composition of the barrier layer on the surface bordering the active layer, from 1 to 0.65.

The resulting test characteristics of the semiconductor light-emitting elements are shown in table 1.

Examples confirm the high efficiency of radiation in the shortwave ultraviolet radiation.

To implement the method used conventional simple industrial equipment, which makes the invention according to the criterion of "industrial p is inanimate".

The semiconductor element emitting light in the ultraviolet range, the structure of which sequentially includes a substrate, a buffer layer made of a nitride material, an n-contact layer made of a nitride-based material doped with Si, an active layer on the one or more quantum wells made of a nitride material, a barrier layer made of Al_XGa_1-XN doped with Mg, and p-contact layer made of a nitride-based material doped with Mg, characterized in that the nitride material of the n-contact layer used Al_YGa_1-YN, in which 0,25≤Y≤0,65, as a nitride material of the active layer used Al_ZGa_1-ZN, where Y-0,08≤Z≤Y is 0.15, the barrier layer is 0.3≤X≤1, as a nitride material of the p-contact layer used Al_WGa_1-WN, where Y≤W≤0,7, while the active layer is doped with Si a Si concentration not less than 10¹⁹cm³width d of quantum wells in the active layer is 1≤d≤4 nm, the mole fraction of A1 on the surface of the barrier layer adjacent to the active layer is from 0.6 to 1, and further reduced by the thickness of the barrier layer to the boundary with the p-contact layer with a gradient from 0.02 to 0.06 to 1 nm thickness of the barrier layer, and the width b of the barrier layer is within a 10≤b≤3 nm.