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p-type doping GaN Lee Yong Hee

p-type doping GaN Lee Yong Hee. GaN 박막의 물성 안정상인 Wurtzite 구조와 준안정상인 Zincblende 구조 ( 결정학적 특성 ) Eg=3.39 eV ( 광학적 특성 ) V N 로 인하여 n- 형 존재 ( 전기적 특성 ) 열화적으로 매우 안정 . 경도 높다. GaN 계 질화물 반도체의 특성 1.9eV(InN)~6.2eV(AlN) 의 직접천이형 에너지 밴드갭으로 가시광선 ~UV 파장영역 가지고 있다. Common Dopants for Ⅲ-Nitrides

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p-type doping GaN Lee Yong Hee

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  1. p-type doping GaN Lee Yong Hee

  2. GaN 박막의 물성 • 안정상인 Wurtzite 구조와 준안정상인 Zincblende 구조 (결정학적 특성) • Eg=3.39 eV (광학적 특성) • VN로 인하여 n-형 존재 (전기적 특성) • 열화적으로 매우 안정. 경도 높다.

  3. GaN계 질화물 반도체의 특성 • 1.9eV(InN)~6.2eV(AlN)의 직접천이형 에너지 밴드갭으로 가시광선~UV 파장영역 가지고 있다.

  4. Common Dopants for Ⅲ-Nitrides • Donors • -Nitrogen Vacancies • -Oxygen • -Silicon (SiH4, Si2H6사용 / Si replace Ga) • -Germanium • 2. Acceptors • Divalent Atoms (Zn, Cd, Mg, Be) • Tetravalent Atoms (Carbon)

  5. http://www.onr.navy.mil/sci_tech/information/312_electronics/ncsr/materials/default.asphttp://www.onr.navy.mil/sci_tech/information/312_electronics/ncsr/materials/default.asp

  6. p-type doping in Gallium Nitride Magnesium is currently the main p-type dopant used for nitrides. Unfortunately, Its large ionization energy 210meV, poses severe limitations. [Mater. Sci. Engin. B 59, 211 (1999)] About 1020cm-3 Mg acceptors can be incorporated in GaN, but at room temperature, The hole concentration is only on the order to 1018cm-3. Increasing the Mg concentration dose not improve the conductivity; in fact, it leads to lower hole concentration. [Mater. Res. Soc. Symp. Proc. 449, 509 (1997)] It has been suggested that the solubility limit of Mg in GaN plays an important role In this limitation. The solubility is limited due to competing formation of Mg3N2. Trying to push the Mg concentration in GaN beyond this limit may result in precipitation of Mg3N2, which may be responsible for a decrease in crystal quality and the observed reduction in hole concentration.Incorporation of Mg on interstitial sites (Mgi) or antisites (MgN) is unlikely to be a problem, given the high formation energies of these species. [Mater. Res. Soc. Symp. Proc. 395, 645 (1996)] http://www.onr.navy.mil/sci_tech/information/312_electronics/ncsr/materials/default.asp

  7. p-type doping in Gallium Nitride Hydrogen plays an important role in p-type doping of GaN; indeed, many of the common Growth techniques for GaN introduce large quantities of hydrogen into the growth environment. [phys. Rev. Lett. 75, 4452 (19995)] Hydrogen prefers the positive charge state in p-type material, acting as a donor; it prefers the Negative charge state in n-type material, acting as an acceptor. Hydrogen is thus an amphoteric Impurity and always counteracts the prevailing conductivity of the semiconductor. This is similar to the behavior of hydrogen in other semiconductors such as silicon and GaAs. Nitrogen vacancies could in principle act as compensating centers in p-type GaN. In the Presence of hydrogen, however, compensation by nitrogen vacancies is suppressed. Indeed , the formation energy of hydrogen is lower than that of nitrogen vacancies, and hence hydrogen is more likely to incorporate as the compensating donor, in the process reducing the concentration of nitrogen vacancies. Another beneficial effect due to hydrogen is an increase in the solubility of the acceptor. [Appl. Phys. Lett. 68, 1829 (1996)] After growth, the material contains equal concentrations of Mg and H, and is thus electrically inactive; however, the binding energy of H to Mg, and the migration barrier for H diffusion are low enough to allow hydrogen to be removed from the vicinity of the acceptors by a thermal annealing procedure.Such an activation anneal is indeed well known to be necessary render the Mg acceptors electrically active http://www.onr.navy.mil/sci_tech/information/312_electronics/ncsr/materials/default.asp

  8. ■ Magnesium doping • Cp2Mg, MeCp2Mg • Mg replace Ga • Zn dopant 문제 -> Mg 대체 • Incorporation ratio가 온도에 무관 • High sticking coefficient / low vapor pressure of Cp2Mg • as-grown 상태에서 Inactivation. • Mg-H 의 분리를 위해 N2분위기에서 어닐링 / 약 2%정도 활성화되고 • 대부분 Mg-H bonding이 되어 있다.

  9. ref) Journal of Crystal Growth 193 (1998) 300

  10. ref) Journal of Crystal Growth 193 (1998) 300

  11. 일반적 성장된 GaN박막의 경우 n-type 특성 지니고 있는데 이는 성장시 1:1 화학 양론비를 맞추도록 충분한 N이 인입되지 않았기 때문에 발생하는 결합에 의한 것으로 보임. 최근 성장 중 불순물로 인입되는 산소의 영향도 배제할 수 없음이 밝혀지고 있음. p-type 도핑의 제어는 어려운데, 다른 물질에 비해 3-5족 질화물 반도체의 이온결합 특성이 강하여 분순물 주입시 불순물의 에너지 준위가 높기 때문. 특히 p-type 불순물의 활성화는 200meV이상의 에너지를 필요하므로 활성화 율이 낮고 정공 이동도도 매우 낮다. 따라서 p-type 도핑을 위해서 Mg, Zn, Cd 등의 여러가지 물질 들이 연구 되고 있음. 또한 p-type dopant들은 공정중에 발생하는 수소와 complex를 형성하여 전기적 특성을 저해하며 활성화를 방해. 수소를 탈착시켜 p-type 전하를 활성하기 위해 LEEBI(low energy electron beam irrAdation) 이나 질소 분위기 열처리를 이용한다.

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