Hidrogen Passivasi Impuritas Karbon dalam GaN Doped Mg, Meningkatkan Performa p-GaN
Abstrak
Efek hidrogen yang tidak sengaja di-dope terhadap properti contoh p-GaN doped Mg yang tumbuh melalui metal-organic chemical vapor deposition (MOCVD) diteliti melalui room temperature photoluminescence (PL) dan Hall dan secondary ion mass spectroscopy (SIMS) pengukuran. Ditemukan bahwa ada interaksi antara residual hydrogen dan carbon impurities. Peningkatan carbon doping concentration dapat meningkatkan resistivity p-GaN dan melemahkan blue luminescence (BL) band intensity. Namun, ketika hydrogen incorporation meningkat dengan carbon doping concentration, peningkatan resistivity disebabkan oleh carbon impurity melemah dan BL band intensity ditingkatkan. Ini menunjukkan bahwa co-doped hydrogen tidak hanya passivate MgGa, tetapi juga dapat passivate carbon impurities dalam Mg-doped p-GaN.
Pendahuluan
GaN-based third-generation semiconductor materials dan legasinya telah menarik perhatian besar [1] karena aplikasi luas termasuk light-emitting diodes (LEDs) [2,3,4] dan laser diodes (LDs) [5,6,7]. Meskipun GaN-based photonic devices widely commercialized, relatively low hole concentration dan high resistivity p-type GaN masih secara signifikan membatasi performa perangkat tersebut [8, 9]. Banyak penelitian telah down untuk improve p-type doping efficiency untuk III-nitrides [10, 11]. Hydrogen dan carbon adalah dua main residual impurities yang ada dalam metal-organic chemical deposition (MOCVD)-grown Mg-doped GaN epilayers. Diketahui bahwa hydrogen impurities dapat passivate Mg dalam p-GaN [12]. Di sisi lain, carbon impurities dapat membentuk banyak jenis defec dan meningkatkan resistivity Mg-doped p-GaN. Banyak penelitian telah done untuk decrease hydrogen dan carbon impurities. Namun, sedikit penelitian tentang interaction antara hydrogen dan carbon impurities.
Diketahui bahwa terlalu banyak residual impurity baik hydrogen maupun carbon dapat menyebabkan high resistivity in as-grown Mg-doped GaN films. Karena H-containing MOCVD growth environment, Mg selalu passivated by hydrogen impurities, dan neutral Mg–H bond complex dapat terbentuk selama film growth [13]. Untungnya, in remarkable way, Nakamura et al. [12] group telah pertama kali menunjukkan bahwa rapid thermal annealing in N2 ambient pada suhu > 700 °C dapat berhasil dissociate Mg–H complexes dan efektif remove hydrogen atoms dari Mg-doped GaN films.
Untuk beberapa tahun terakhir, dengan research dan development long-wavelength multiple-quantum-well (MQW) devices, high-indium-content InGaN/GaN layers telah widely digunakan sebagai active layers. Untuk avoid segregation dan structural degradation MQW, relatively low growth temperature (< 1000 °C) dan relatively low rapid thermal annealing temperature diperlukan. Namun, unintentionally doped carbon impurity concentration meningkat dengan decreasing growth temperature, yang mengarah ke higher concentration carbon impurity-related defects dalam GaN, existing dalam forms substitutional defects (CN), interstitial defects (Ci), dan complexes [14, 15]. Defek ini dapat act sebagai either donors atau deep-acceptor species dan meningkatkan resistivity p-GaN secara signifikan [16]. Akibatnya, low-temperature (LT)-grown Mg-doped p-type GaN films sering show higher resistivity dibandingkan those grown at higher temperature. Berlawanan dengan harapan kami, research kami menemukan bahwa p-GaN films dengan both high concentration hydrogen dan carbon impurities show relatively low resistivity.
Dalam pekerjaan ini, tiga set Mg-doped GaN films dengan different concentrations hydrogen dan carbon residual impurities diteliti melalui secondary ion mass spectroscopy (SIMS), photoluminescence (PL), dan Hall measurements. Ditemukan bahwa hydrogen dapat passivate carbon impurities dalam p-GaN, which points out new direction untuk grow high-quality p-type GaN film.
Metode Eksperimen
Masih belum diketahui bagaimana mengontrol residual hydrogen concentration dengan setting MOCVD growth conditions. Jadi, sampel kami dibagi ke dalam different groups berdasarkan SIMS results daripada growth conditions, similar Mg concentration di setiap group.
Dalam pekerjaan ini, banyak Mg-doped GaN films ditumbuhkan pada 2-μm-thick unintentionally doped GaN layer template dalam metal-organic chemical vapor deposition (MOCVD) system. Trimethylgallium (TMGa), ammonia (NH3), dan bis-cyclopentadienyl-magnesium (Cp2Mg) digunakan sebagai precursors untuk Ga, N, dan Mg, masing-masing. Growth temperature semua p-GaN samples relatively low pada 1020 °C. Mg doping concentration mainly disesuaikan oleh Cp2Mg flow rate. Residual carbon impurity concentration mainly disesuaikan oleh NH3 flow rate selama MOCVD—more NH3 corresponds to less carbon impurity [17]. Rapid thermal annealing dilakukan dalam nitrogen environment pada suhu 800 °C selama 3 min untuk de-passivate Mg–H complexes.
Hall test dilakukan untuk measure resistivity p-GaN samples. Untuk make ohmic contact on p-type GaN, molten indium metal pointed pada sample surface dan acts sebagai metal electrode. Untuk check concentrations magnesium, hydrogen, carbon, dan oxygen impurities, [Mg], [C], [H], [O], secondary ion mass spectroscopy (SIMS) measurements of these p-GaN samples diambil. Seven samples dipilih karena suitable Mg concentration dan divided into three groups, similar Mg concentration di setiap group, named as A1, A2, A3, B1, B2, dan C1, C2.
Room temperature photoluminescence (PL) measurements semua contoh dilakukan oleh 325-nm wavelength He–Cd laser pada excitation density sekitar 0.4 W/cm2. Luminescence intensity dinormalisasi oleh near-band-edge emission luminescence intensity (at around 3.44 eV)1 untuk analysis.
Hasil dan Pembahasan
Hasil Hall test dan SIMS measurement ditampilkan dalam Table 1. Berdasarkan SIMS results Mg, C, dan H concentration measurements, tujuh contoh divided into three groups A, B, dan C. Samples di setiap group harus similar Mg concentration, because Mg major acceptor in p-GaN dan conductivity p-GaN mostly caused by Mg. Jadi, if we want investigate influence H dan C impurity on resistivity, we should keep Mg concentration invariability di setiap group. Joint influence doping concentrations impurities ini pada sample property, mainly p-type electrical resistivity, dianalisis. Doping concentration magnesium in these samples very high (in 1019~3 × 1019 cm−3) dan has no remarkable difference untuk samples di setiap group. Oxygen concentration low enough (1016 cm−3) dan can be taken out dari further consideration.
In group A, rise carbon impurities causes tremendous resistivity increase p-GaN, while in group B, increase hydrogen along with carbon impurities found to weaken trend ini. Dan group C employed untuk further investigate influence on BL band.
Dapat terlihat dalam Table 1 dan Fig. 1 bahwa untuk samples A1–A3, carbon impurity concentration increases dramatically, changing two orders of magnitude from 1.17 × 1017 to 1.12 × 1019 cm− 3, but concentrations magnesium, hydrogen, dan oxygen change only little. Dari previous research, we realized bahwa though doping concentration magnesium very high, actually hole concentration still two orders of magnitude lower than magnesium because low ionization rate dan high possibility self-compensation [18, 19]. In GaN, MgGa has acceptor ionization energy 260 meV [20], order of magnitude more than kBT (about 26 meV) pada room temperature, dan defects dan impurities yang ada dalam GaN can compensate atau passivate MgGa, sehingga hole concentration in Mg-doped GaN about two orders of magnitude lower than magnesium. In addition, residual carbon impurities juga can cause negative effects p-type GaN conductivity [16]. Resistivity p-GaN samples in series A raised obviously with increasing carbon concentration (from 1.39 to ~ 47.7 Ω cm). Oleh karena itu, differences between samples A1–A3 dapat attributed to difference carbon impurities. As described in our previous study [16], carbon impurities may preferentially play role donor-type compensation centers dalam Mg-doped GaN films. Donors can compensate magnesium acceptors. Oleh karena itu, resistivity p-GaN meningkat dengan rise residual carbon impurities concentration.
Resistivity samples changes dengan C concentration di groups A dan B
Di sisi lain, in series B, concentrations magnesium dan oxygen change little di setiap group as shown in Table 1 dan Fig. 1. Carbon concentration sample B1 much higher (about 20 times) daripada sample B2. Namun, resistivity sample B2 quite close dan not much larger daripada sample B1. Tren ini berbeda dari what we have observed untuk group A. Hence, it suggests this different trend resistivity variation in two groups may attributed to difference hydrogen impurity concentration. For samples A1–A3, hydrogen impurity concentration decreases little, dengan factor ~ 1/3, sementara carbon impurity concentration increases nearly two orders of magnitude. Sebaliknya, untuk samples B1–B2, concentration hydrogen impurity increases along dengan carbon impurity. Thus, obtained result suggests hydrogen incorporation may weaken influence of carbon pada resistivity Mg-doped p-GaN, producing counteraction effect.
Untuk further investigate how carbon impurity compensates magnesium acceptors dan why hydrogen can weaken process ini, room temperature photoluminescence measurements dilakukan. In Fig. 2a, as shown by PL measurement results samples A1~A3, luminescence peak at about 2.9 eV can be seen obviously. This blue luminescence (BL) band telah studied for decades. Diketahui bahwa BL band in p-GaN PL spectra around 2.9 eV has distinct donor–acceptor pair luminescence character. Untuk candidate acceptor, isolated Mg substitute Ga defect (MgGa) adalah natural choice. Dan most possible candidate untuk deep donor in very heavily Mg-doped GaN adalah nearest neighbor complex, which is associate MgGa dan nitrogen vacancy (VN), formed by self-compensation [21]. As integral intensity BL band decreases dengan higher doping carbon impurities (Fig. 2b), we can assume carbon impurities may decrease number relevant donor–acceptor pairs by compensating magnesium acceptors, because carbon impurities may preferentially play role donor-type compensation centers in Mg-doped GaN films [16]. Appearance strong 2.2-eV peak untuk sample A3 indicates ada larger number carbon-related defects in sample A3 [15].
a Hasil normalized PL intensity samples A1~A3. b Integral PL (solid triangle) intensity dan C (solid square) dan H (solid circle) concentrations untuk samples A1~A3. c Hasil normalized PL intensity samples B1 dan B2
Sementara itu, regardless large increase both carbon dan hydrogen concentrations from B1 to B2 in sample group B, PL spectra these two samples quite similar each other. Actually, there is no obvious BL band in sample B1 dan only small BL peak in sample B2 (Fig. 2c), perhaps because relatively lower concentration magnesium in series B samples (nearly 1 × 1019 cm−3) in comparison with group A samples. Therefore, data samples C1 dan C2 employed untuk check interaction between hydrogen dan carbon impurities further.
It is noted Mg dan C concentrations in sample C1 similar to those in sample C2, dan resistivity two samples also similar each other. Tetapi interesting untuk note bahwa BL band changes obviously in PL spectra sample group C.
H concentration in sample C2 tiga kali higher daripada sample C1. Figure 3a shows BL band intensity quite different untuk samples C1 dan C2. Intensity BL band C2 much larger, attributed to larger hydrogen concentration in this sample. Additionally, integral intensity BL band increases clearly dengan rise concentration hydrogen, although carbon impurity (can decrease BL band) concentration also increases little at same time (Fig. 3b). It implies reason increase BL band adalah increase hydrogen impurities daripada carbon. It suggests hydrogen dan carbon may have opposite effect pada BL band p-GaN. Untuk hydrogen impurities, we assume most probable way enhance BL band adalah form more relevant donor–acceptor pairs by forming C–H complexes with carbon impurity dan passivating carbon impurities in Mg-doped GaN. So, it is speculated hydrogen can form complexes with carbon in Mg-doped p-GaN sample, leading to smaller concentration donor-type compensation centers. In other words, hydrogen can passivate carbon dan improve conductivity Mg-doped p-GaN. Further investigation needed untuk figure out how to control hydrogen incorporation to preferentially passivate carbon impurity instead of Mg acceptors.
a Normalized PL intensity samples C1 dan C2. b Integral PL intensity dan C dan H concentration untuk samples C1 dan C2
Kesimpulan
In summary, effects carbon dan hydrogen impurities on Mg-doped GaN films diteliti. Ditemukan bahwa carbon impurities may preferentially play role donor-type compensation centers dan compensate Mg acceptor in Mg-doped GaN films. Increase carbon doping concentration can increase resistivity p-GaN dan weaken blue luminescence (BL) band intensity. Namun, ketika hydrogen incorporation increased dengan carbon doping concentration, increase resistivity caused by carbon impurity is weaken dan BL band intensity enhanced, which suggests hydrogen not only can passivate MgGa acceptors, tetapi juga may passivate carbon by forming C–H complex with carbon impurity.
Ketersediaan Data dan Bahan
Datasets used dan/atau analyzed during current study available from corresponding author on reasonable request.
