| 1. |
- Chen, Ding-Yuan, 1991, et al.
(författare)
-
Structural investigation of ultra-low resistance deeply recessed sidewall ohmic contacts for AlGaN/GaN HEMTs based on Ti/Al/Ti-metallization
- 2023
-
Ingår i: Semiconductor Science and Technology. - : IOP Publishing Ltd. - 1361-6641 .- 0268-1242. ; 38:10
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents a novel approach to forming low-resistance ohmic contacts for AlGaN/GaN HEMTs. The optimized contacts exhibit an outstanding contact resistance of approximately 0.15 & omega;& BULL;mm. This is achieved by firstly recessing the barrier of the heterostructure to a depth beyond the channel. In this way, the channel region is exposed on the sidewall of the recess. The coverage of the Ti/Al/Ti ohmic metalization on the sidewall is ensured through tilting of the sample during evaporation. The annealing process is performed at a low temperature of 550 & DEG;C. The approach does not require precise control of the recess etching. Furthermore, the method is directly applicable to most barrier designs in terms of thickness and Al-concentration. The impact of recessed sidewall angle, thickness and ratio of Ti and Al layers, and the annealing procedure are investigated. Structural and chemical analyses of the interface between the ohmic contacts and epi-structure indicate the formation of ohmic contacts by the extraction of nitrogen from the epi-structure. The approach is demonstrated on HEMT-structures with two different barrier designs in terms of Al-concentration and barrier thickness. The study demonstrate large process window in regard to recess depth and duration of the annealing as well as high uniformity of the contact resistance across the samples, rendering the approach highly suitable for industrial production processes.
|
|
| 2. |
- Ding Yuan, Chen, 1991, et al.
(författare)
-
Impact of in situ NH3 pre-treatment of LPCVD SiN passivation on GaN HEMT performance
- 2022
-
Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 37:3
-
Tidskriftsartikel (refereegranskat)abstract
- The impact on the performance of GaN high electron mobility transistors (HEMTs) of in situ ammonia (NH3) pre-treatment prior to the deposition of silicon nitride (SiN) passivation with low-pressure chemical vapor deposition (LPCVD ) is investigated. Three different NH3 pre-treatment durations (0, 3, and 10 min) were compared in terms of interface properties and device performance. A reduction of oxygen (O) at the interface between SiN and epi-structure is detected by scanning transmission electron microscopy (STEM )-electron energy loss spectroscopy (EELS) measurements in the sample subjected to 10 min of pre-treatment. The samples subjected to NH3 pre-treatment show a reduced surface-related current dispersion of 9% (compared to 16% for the untreated sample), which is attributed to the reduction of O at the SiN/epi interface. Furthermore, NH3 pre-treatment for 10 min significantly improves the current dispersion uniformity from 14.5% to 1.9%. The reduced trapping effects result in a high output power of 3.4 W mm(-1) at 3 GHz (compared to 2.6 W mm(-1) for the untreated sample). These results demonstrate that the in situ NH3 pre-treatment before LPCVD of SiN passivation is critical and can effectively improves the large-signal microwave performance of GaN HEMTs.
|
|
| 3. |
- Gogova, Daniela, et al.
(författare)
-
Epitaxial growth of β -Ga 2 O 3 by hot-wall MOCVD
- 2022
-
Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5, s. 055022-055022
-
Tidskriftsartikel (refereegranskat)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and highperformance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth ofβ-Ga2O3. Epitaxial β-Ga2O3 layers at high growth rates (above 1 μm/h), at low reagent flows, and at reduced growth temperatures(740 ○C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. Thehot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial β-Ga2O3 layers are demonstrated with a 201 ¯rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) ¯ β-Ga2O3 substrates, indicative ofsimilar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be furtherexplored for the fabrication of β-Ga2O3
|
|
| 4. |
- Gogova, Daniela, 1967-, et al.
(författare)
-
Epitaxial growth of β-Ga2O3 by hot-wall MOCVD
- 2022
-
Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5
-
Tidskriftsartikel (refereegranskat)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of beta-Ga2O3. Epitaxial beta-Ga2O3 layers at high growth rates (above 1 mu m/h), at low reagent flows, and at reduced growth temperatures (740 degrees C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial beta-Ga2O3 layers are demonstrated with a 201 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) beta-Ga2O3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of beta-Ga2O3.
|
|
| 5. |
- Gustafsson, Anders, et al.
(författare)
-
Cathodoluminescence investigations of dark-line defects in platelet-based InGaN nano-LED structures
- 2024
-
Ingår i: Nanotechnology. - : IOP Publishing Ltd. - 0957-4484 .- 1361-6528. ; 35:25
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the optical properties of heterostructured InGaN platelets aiming at red emission, intended for use as nano-scaled light-emitting diodes. The focus is on the presence of non-radiative emission in the form of dark line defects. We have performed the study using hyperspectral cathodoluminescence imaging. The platelets were grown on a template consisting of InGaN pyramids, flattened by chemical mechanical polishing. These templates are defect free, whereas the dark line defects are introduced in the lower barrier and tend to propagate through all the subsequent layers, as revealed by the imaging of different layers in the structure. We conclude that the dark line defects are caused by stacking mismatch boundaries introduced by multiple seeding and step bunching at the edges of the as-polished, dome shaped templates. To avoid these defects, we suggest that the starting material must be flat rather than dome shaped.
|
|
| 6. |
- Gustafsson, Anders, et al.
(författare)
-
Cathodoluminescence investigations of dark-line defects in platelet-based InGaN nano-LED structures
- 2024
-
Ingår i: Nanotechnology. - : IOP Publishing Ltd. - 0957-4484 .- 1361-6528. ; 35:25
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the optical properties of heterostructured InGaN platelets aiming at red emission, intended for use as nano-scaled light-emitting diodes. The focus is on the presence of non-radiative emission in the form of dark line defects. We have performed the study using hyperspectral cathodoluminescence imaging. The platelets were grown on a template consisting of InGaN pyramids, flattened by chemical mechanical polishing. These templates are defect free, whereas the dark line defects are introduced in the lower barrier and tend to propagate through all the subsequent layers, as revealed by the imaging of different layers in the structure. We conclude that the dark line defects are caused by stacking mismatch boundaries introduced by multiple seeding and step bunching at the edges of the as-polished, dome shaped templates. To avoid these defects, we suggest that the starting material must be flat rather than dome shaped.
|
|
| 7. |
|
|
| 8. |
- Kehoe, Laura, et al.
(författare)
-
Make EU trade with Brazil sustainable
- 2019
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 9. |
- Knight, Sean Robert, et al.
(författare)
-
Room temperature two-dimensional electron gas scattering time, effective mass, and mobility parameters in AlxGa1−xN/GaN heterostructures (0.07 ≤ x ≤ 0.42)
- 2023
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics Inc.. - 0021-8979 .- 1089-7550. ; 134:18
-
Tidskriftsartikel (refereegranskat)abstract
- Al xGa 1−xN/GaN high-electron-mobility transistor (HEMT) structures are key components in electronic devices operating at gigahertz or higher frequencies. In order to optimize such HEMT structures, understanding their electronic response at high frequencies and room temperature is required. Here, we present a study of the room temperature free charge carrier properties of the two-dimensional electron gas (2DEG) in HEMT structures with varying Al content in the Al xGa 1−xN barrier layers between x=0.07 and x=0.42. We discuss and compare 2DEG sheet density, mobility, effective mass, sheet resistance, and scattering times, which are determined by theoretical calculations, contactless Hall effect, capacitance-voltage, Eddy current, and cavity-enhanced terahertz optical Hall effect (THz-OHE) measurements using a low-field permanent magnet (0.6 T). From our THz-OHE results, we observe that the measured mobility reduction from x=0.13 to x=0.42 is driven by the decrease in 2DEG scattering time, and not the change in effective mass. For x<0.42, the 2DEG effective mass is found to be larger than for electrons in bulk GaN, which in turn, contributes to a decrease in the principally achievable mobility. From our theoretical calculations, we find that values close to 0.3 m0 can be explained by the combined effects of conduction band nonparabolicity, polarons, and hybridization of the electron wavefunction through penetration into the barrier layer.
|
|
| 10. |
|
|
